Tuesday 18 March 2014

Monday 17 March 2014

DERIVATION OF CENTROID OF TRIANGLE

DERIVATION OF CENTROID OF TRIANGLE

IMPORTANT QUESTION QUADRATIC EQUATIONS CLASS X

In  a flight of 600 km an aircraft was slowed........

IMPORTANT QUESTION QUADRATIC EQUATIONS CLASS X

FROM A STATION, TWO TRAINS START AT THE SAME TIME ONE TRAIN.......

IMPORTANT QUESTION QUADRATIC EQUATIONS CLASS X

A student scored a total of 32 marks in class tests ........

IMPORTANT QUESTION VSA CLASS X

From a solid cylinder whose height is 2.4 cm .....

IMPORTANT QUESTION VSA CLASS X

A vessel is in form of a hemishpherical....

IMPORTANT QUESTION VSA CLASS X

A tent is of shape of aright circular cylinder....

IMPORTANT QUESTION AREA RELATED TO CIRCLES CLASS X

FIND THE AREA OF THE SHADED REGION WHERE ABCD IS A SQUARE OF SIDE 10 CM.

IMPORTANT QUESTION AREA RELATED TO CIRCLES CLASS X

ABCP is a quadrant of a circles of radius 14cm with AC as a diameter a semicircle is drawn. Find the area of the shaded region

IMPORTANT QUESTION AREA RELATED TO CIRCLES CLASS X

Find the area of shaded region where radii of the two concentric circles with centres O are 7cm abd 14 cm resp and <AOC=40°

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

From the top of a light house, the angles of depression of two ships on the opposite sides......

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

The angle of elevation of the top of the building from the foot of the tower is 30° and...............

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

The angle of elevation of a cloud from a point....

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

The angle of elevation of a jet plane.......

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

A man standing on the deck ...... Cool ques..

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

Sunday 16 March 2014

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

IMPORTANT QUESTION SOME APPS OF TRIGO CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

IMPORTANT QUESTION AP CLASS X

CLASS X अब कहाँ दूसरों के दुःख में दुःखी होने वाल Q/A


प्रश्न १: प्रकृति में आए असंतुलन का क्या परिणाम हुआ?
उत्तर : प्रकृति में आए असंतुलन का यह परिणाम हुआ कि कोई भी प्रदूषण
के प्रभाव से अछूता नहीं रहा | पक्षियों ने बस्तियों से भागना शुरू कर दिया |
गर्मियों में ज़्यादा गर्मी, बेवक्त की बरसातें, भूकंप, सैलाब, तूफ़ान, ज़लज़ले
और नित नए रोगों के रूप में हम इस असंतुलन के प्रभाव को स्पष्ट देख सकते
हैं | प्रकृति की सहनशक्ति की एक सीमा होती है और जब उसके साथ
अत्यधिक छेड़छाड़ की जाती है, तो प्रकृति में असंतुलन पड़ जाता है | इससे
पर्यावरण पर बुरा प्रभाव पड़ता है |
प्रश्न २: लेखक की माँ ने पूरे दिन रोज़ा क्यों रखा ?
उत्तर : लेखक की माँ ने पूरे दिन का रोज़ा रखा ताकि वह अपनी भूल
का प्रायश्चित कर सके | लेखक के ग्वालियर के घर में एक कबूतर के जोड़े ने
अपना घोंसला बना लिया था, जिसमें रखे दो अण्डों में से एक बिल्ली ने तोड़
दिया था | लेखक की माँ को यह देखकर बहुत दुःख हुआ | उन्होंने स्टूल पर
चढ़कर दूसरे अंडे को बचाने की कोशिश की परन्तु वह अंडा उनके हाथ से
गिरकर टूट गया | कबूतरों की परेशानी और दुःख देखकर माँ की आँखों में आँसू
आ गए | उस दुःख में उन्होंने कुछ भी खाया-पीया नहीं और बस रोती रहीं |
खुदा से माफी माँगने के लिए उन्होंने पूरे दिन का रोज़ा रखा और नमाज़ पढ़कर
इस गलती को माफ़ करने की दुआएँ मांगती रही |
प्रश्न 3: 'डेरा डालने' से आप क्या समझते हैं ?
उत्तर : डेरा डालने का अर्थ है- अस्थायी निवास | लेखक यह कहना चाहते हैं
कि बढ़ती जनसंख्या के कारण असंख्य बड़ी-बड़ी इमारतों का निर्माण
किया गया | पेड़- पौधों को काटा गया और वनों की भूमि पर
बस्तियाँ बना दी गईं | इससे पशु- पक्षियों के बसेरे छिन गए | उनकी अनेक
प्रजातियाँ समाप्त हो गईं और वे अपना घोंसला छोड़कर यहाँ- वहाँ डेरा डालने
लगे | शहरों में बनी विभिन्न इमारतों के बीच इन्होंने अपने रहने का स्थान
बनाया लेकिन इन घरों में रहने वाले लोगों ने इन्हें वहाँ से भी भगा दिया |
इसका परिणाम यह हुआ कि इन पक्षियों के पास रहने के लिए कोई निश्चित व
स्थायी ठिकाना नहीं है | इसलिए इनकी व्यथा को स्पष्ट करने के लिए लेखक
ने डेरा- डालने जैसे शब्द का प्रयोग किया है |
प्रश्न ४: समुद्र के गुस्से की क्या वजह थी ? उसने अपना गुस्सा कैसे
निकला ?
उत्तर : समुद्र के गुस्से की वजह थी उसका सिमटना | निरंतर
बढ़ती आबादी के कारण बिल्डर धीरे-धीरे समुद्र की ज़मीन छीनकर उसपर
बस्तियाँ बनाते जा रहे थे | समुद्र ने अपने आप को बहुत सिकोड़ा | जब
उसकी सहन-शक्ति की सीमा समाप्त हो गई, तो वह गुस्से से भर उठा | उसने
अपना गुस्सा प्रकट करने के लिए लहरों द्वारा तीन जहाज़ों को बच्चों की गेंद
की तरह उछालकर तीन दिशाओं में फेंक दिया | एक जहाज़ वर्ली के समुद्र के
किनारे जा गिरा, दूसरा बांद्रा के कार्टर रोड के सामने औंधे मुँह जाकर
गिरा और तीसरा गेटवे ऑफ इंडिया पर गिरा | ये तीनों जहाज़ अनेक
कोशिशों के बाद भी चलाने लायक नहीं हो सके |
प्रश्न ५: " जो जितना बड़ा होता है, उसे उतना ही कम गुस्सा आता है |"
आशय स्पष्ट करें |
उत्तर : प्रस्तुत कथन का आशय यह है की बड़ा व्यक्ति सदैव उदार हृदय
होता है | लेखक कहना चाहते हैं कि महान व बड़े व्यक्ति में कई गुणों का संगम
होता है | उनमें से एक गुण यह है कि वे सहनशील होते हैं और अपने क्रोध पर
नियंत्रण करना जानते हैं |
उन्हें सामान्यतः क्रोध नहीं आता परन्तु जब आता है तो उसपर नियंत्रण
करना कठिन है | समुद्र इसका सबसे बड़ा उदाहरण है | ऊपर से शांत और
गंभीर दिखने वाले सागर को जब गुस्सा आता है, तो वह प्रलय का दृश्य
प्रस्तुत कर देता है | इसका सजीव उदाहरण मुंबई के पास देखने को मिला था,
जब सागर ने अपने ऊपर तैरने वाले तीन जहाज़ों को उछालकर बुरी तरह तहस-
नहस कर दिया था |

CLASS X बड़े भाई साहब Q/A

बड़े भाई साहब
प्रश्न १: कथा नायक की रुचि किन कार्यों में थी?
उत्तर: कथा-नायक में बुद्धि की कमी न थी, परन्तु उसका मन पढ़ने
की अपेक्षा खेल में ही लगा रहता था | उसे खेलना-
कूदना कंकरियाँ उछालना, गप्पें मारना, कागज़ की तितलियाँ उड़ाना,
चारदीवारी पर चढ़कर कूदना और फाटक पर सवार होकर उसे मोटरकार
की तरह चलाना बहुत भाता था |
प्रश्न २: बड़े भाई साहब छोटे भाई से पहला सवाल क्या पूछते थे?
उत्तर : वे हमेशा उससे पूछते थे कि 'कहाँ थे' |
प्रश्न ३: दूसरी बार पास होने पर छोटे भाई के व्यवहार में
क्या परिवर्तन आया?
उत्तर : छोटे भाई के दूसरी बार पास होने और बड़े भाई के फिर से फेल
होने पर छोटे भाई की स्वच्छंदता बढ़ गई और उसने अपना अधिक समय
मौज-मस्ती करने में व्यतीत किया | उसने बड़े भाई
की सहिष्णुता का अनुचित लाभ उठाना आरंभ कर दिया |
प्रश्न ४: बड़े भाई साहब लेखक से उम्र में कितने बड़े थे और वे कौन
सी कक्षा में पढ़ते थे ?
उत्तर: बड़े भाई साहब लेखक से उम्र में पाँच वर्ष बड़े थे और वे नवीं कक्षा में
पढ़ते थे |
प्रश्न ५: बड़े भाई साहब दिमाग को आराम देने के लिए क्या करते थे?
उत्तर : बड़े भाई साहब दिमाग को आराम देने के लिए कापियों और किताबों के
हाशियों पर चिड़ियों, कुत्तों, बिल्लियों आदि के चित्र बनाते थे और अर्थहीन
बातें लिखते थे | कभी-कभी सुन्दर लिखी में शेर भी लिखते थे |
प्रश्न ६: बड़े भाई साहब को अपने मन की इच्छाएँ क्यों दबानी पड़ती थीं?
उत्तर : बड़े भाई साहब को अपने मन की इच्छाएँ दबानी पड़ती थीं क्योंकि वह
स्वयं को अपने भाई के समक्ष आदर्श रूप में प्रस्तुत करना चाहते थे |
बड़ा होने का दायित्व बोध उन्हें इच्छा होते हुए भी खेल कूद में समय गंवाने से
रोकता था | वे चाहे पढ़ाई में पीछे रह गए हों पर सहज-बुद्धि की उनमें कमी न
थी | वे जानते थे कि अगर वे स्वयं बरह चलेंगे तो भाई को उसपर चलने से
कैसे रोकेंगे ?
उन्हें ज्ञात था की उनके दादा ने बड़ी मुश्किलों का सामना कर उन्हें व छोटे
भाई को पढ़ने के लिए छात्रावास भेजा है | वे चाहते थे कि कम से कम एक भाई
तो पढ़ाई में अव्वल आकर उनके पैसे सार्थक करे | वे स्वयं इतने प्रखर-
बुद्धि न थे इसलिए छोटे भाई से अपेक्षा करते थे कि वह कक्षा में अव्वल
आयें | छोटे भाई के समक्ष एक मिसाल बनने के कारण उनका स्वयं का बचपन
ही कहीं खो गया था |
प्रश्न ७: बड़े भाई की डांट-फटकार अगर छोटे भाई को न मिलती तो क्या वह
अव्वल आता ?
उत्तर : बड़े भाई की डांट-फटकार के कारण ही छोटा भाई पढ़ाई
को थोड़ा बहुत समय देता | बड़े भाई के बार-बार डांटने से ही छोटे भाई ने
टाइम-टेबल बनाया था और पढने में ध्यान दिया | बड़े भाई साहब की डांट के
कारण ही उसपर थोड़ा सा अंकुश रहता और वह एक घंटे के करीब पढ़ता |
हालांकि छोटा भाई बुद्धिमान था, परन्तु यह भी सत्य है की बुद्धिमान छात्र
भी परिश्रम करने पर ही सफल होते हैं | भाग्य भी मेहनती का ही साथ
देता है | केवल भाग्य के भरोसे बैठे रहकर छोटा भाई अव्वल न आता |
प्रश्न ८: बड़े भाई साहिब ने जिन्दगी के अनुभव में किसे महत्त्वपूर्ण
कहा है?
उत्तर : बड़े भाई साहब ने किताबी ज्ञान से अधिक महत्त्वपूर्ण ज़िन्दगी के
अनुभव को कहा है क्योंकि जानकारियाँ रख लेना एक बात है और
ज़िन्दगी को सुचारू रूप से व्यतीत करना दूसरी बात | उनके अनुसार जीवन
की सही समझ अनुभव से ही विकसित होती है | किताबें केवल ज्ञान पाने
का माध्यम हैं जबकि अनुभव व्यावहारिक ज्ञान देता है जिसकी कदम-कदम
पर आवश्यकता होती है| संकट के समय बिना घबराये स्थिर-बुद्धि से
उसका सामना करना और सही निर्णय लेना , किताबों से नहीं अपितु अनुभव से
सीखा जा सकता है | बड़े भाई साहब अपने दादा का उदाहरण देते हुए कहते हैं
कि उन्होंने बड़े कम पैसों में बहुत सम्मान और नेकनामी से अपने कुटुम्ब
का पालन किया | हैडमास्टर साहब की अनपढ़ माँ में भी वे गुण थे
जो ऑक्सफ़ोर्ड से शिक्षित हैडमास्टर साहब में नहीं थे | इसी कारण बड़े भाई
साहब का यह दृढ़ विश्वास था कि समझ अनुभवों से आती है, किताबें पढ़ने से
नहीं | सही और गलत का अंतर विवेक से आता है जो किताबों से प्राप्त
नहीं होता |

CLASS X JULIUS CAESAR Q/A

Q1: Describe the role of mob in the play Julius
Caesar
Answer:
No doubt citizens of Rome played a crucial role in the
play Julius Caesar. The crowd of commoners that fills
the streets served several dramatic purposes in the play,
specially during the funeral oration.
Brutus logically gave his reasons that necessitated
Caesar’s death. He informed the commoners that he
acted out of love of Rome and his desire to prevent
tyrants from controlling her. The citizens embraced his
words with cheers and understanding. However, their
mood altered when Antony offered his interpretation of
the situation. He passionately described the deeds
Caesar performed in behalf of the citizens of Rome,
which clearly contradicted the opinion of the
conspirators that Caesar was too ambitious. The mob
who lost her individual identity and showed her
inability to deal with intellect and reason. Antony's
speech overwhelmed the people with grief, despair, and
anger for their “beloved” Caesar’s death. It led to brutal
killing of Brutus and other conspirators by the mob.
Although the citizens are important characters in the
play, they are unreliable, emotionally hyped and fickle
in supporting the latest and most impassioned plea for
their “ears.” In the play, we witness the irrational
behavior of citizens-to-mob who think only to benefit
themselves.
Q2: What arguments did Brutus give for killing
Caesar?
Answer:
Brutus thought that Caesar was too ambitious and
would have turned the Romans into slaves. Brutus's
point is that like the serpent's egg Caesar was bound to
hatch into something really dangerous and he would be
easier to deal with while he was still in the egg stage.He
stated although Caesar wasn’t bad, getting a crown
would change his nature! Brutus put Caesar in poor
light saying that Caesar was ambitious and that he did it
for the good of his country and his countrymen.
Q3: What was the conspiracy? Who hatched it?
Answer: The conspiracy was being hatched for the past
many days because Caesar’s non-stop unceasing
ambition agitated the senators. Metellus Cimber, Casca,
Cassius, Trebunious… and others. They   deliberately
asked Caesar to grant a wish. It was to enfranchise
Pubius Cimber. They were well aware that they would
be refused. Metellus Cimber and others had anticipated
that Caesar would deny and they shall use this
unpleasantness and annoyance as an excuse to kill
Brutus had been convinced to join since it was the need
of the hour as democracy was threatened. The
conspirators feared that Caesar would become a
dictator so they requested Brutus – the idealist to join
them as he was a man of the masses.
Q4: Write a character sketch of Caesar
Answer:  Julius Caesar was a stalwart. He was a brave
and valiant warrior. He conquered to expand the
Roman Empire. He added to the treasures of Rome,
defeated the sons of Pompey brought laurels to Rome.
Caesar believed in embracing death like true warrior. He
rejected his wife’s prayers as foolish and opined that
‘death is an inevitable reality.’
He firmly believed in the good of the common man. His
will is an example of the same. In his will he had only
thought about the well-being of masses.(common men)
However there were certain lapses in his character. He
was rigid, haughty and arrogant. He was over ambitious
and in his lust to conquer he forgot that he was going
against republicanism and democracy. He tried the true
qualities of a dictator and this way the flow which
drove him towards his end.
Q5: Summarize Antony's speeches.
Answer:
FIRST SPEECH:
When Antony re-enters after Caesar’s assassination, He
laments the death of the mighty Caesar saying that it
has an incomparable event. He wished for his own
death at the hands of the conspirators and begged
them to kill him so that he could lie beside Caesar.
According to him no other hour, sword or space could
give him a nobler end.
SECOND SPEECH:
Antony describes himself in an unstable condition. It is
dangerous to declare that he wishes to seek revenge. On
the other hand he doesn’t want to defy Caesar by being
considered a psychopath (flatterer). His conscience tells
him that Caesar’s spirit shall grieve to see Antony as a
flatterer making peace with his enemies.
THIRD SPEECH:
In his third speech, Antony expresses his apology for
Caesar’s death. Here he is all alone. He says that Caesar’s
death will bring large scale death and destruction not
only on earth but also in heaven.
Heaven shall join to avenge Caesar’s death. Bloodshed,
death, destruction shall become a common sight for
Romans because the death of mighty Caesar could not
just pass or ignored. Dead bodies shall cry for burial.
FOURTH SPEECH:
In the 4th speech Antony has come to burry Caesar. He
says “he shall not praise him.” But on the contrary talks
about Caesar in such a light that he may be able to
renew the lost faith and love in the hearts of the
country-men for him. He says that Caesar had led the
conquests for the well being of Rome.
A) He had brought many captives home to Rome and
ensured their financial upliftment.
B) Caesar’s heart wept for the poor.
C) On the feast of Lupercal he refused the offer of the
crown 3 times.
Antony stressed upon the fact that the country-men
didn’t love Caesar without a cause, so they must mourn
for him. If they do not so, they have lost their reason
and judgment.
FIFTH SPEECH:
Antony feels pathetic that no one expresses the
reverence due for Caesar’s dead body. He chooses his
words with caution and says that – if he would
encourage MUTINY, RAGE and PROVOCATION he would
wrong Brutus and Cassius. All his words are
provocative. He concludes that he would rather wrong
the dead person. He also gives a hint to them about
Caesar’s will after reading which all the Romans shall
grieve and beg for hair and blood of Caesar to keep as
a precious relic and declare it as a precious possession
for the coming generations. Antony here puts ideas and
words in the mouths of Romans.
SIXTH SPEECH:
In his sixth speech, Antony stirs the emotions of the
Romans by exposing the wounds on Caesar’s dead
body. He lays stress on the wound given by Brutus. It
was “the unkindest cut of all.” How the wound given by
Brutus was not as fatal as the immorality of Brutus and
Brutus’ betrayal had killed Caesar more than the wound.
SEVENTH SPEECH:
Antony emphasizes that revenge should be well-planned
so as to leave a powerful impact. He wanted the mutiny
to have the desired result, a massive movement which
will involve the max. number
EIGHT SPEECH:
In his last speech, Antony reads ‘s will in which Caesar
had promised monetary and physical benefits to each
and every Roman on an equal basis:
1) 75 drachmas
2) His walks, arbors and orchards for recreation.
Antony had provoked the element of mischief present
in every human being. He had ignited a fire in every
heart. Even the reading of the will was the last nail in
the coffin.
Q6: Write a character sketch of Mark Antony.
Answer:
Loyal and faithful: Loyalty to Caesar and reliable
friendship was his the greatest merit. He avenged
Caesar's death which had shattered him.
Intelligent but Cunning and deceitful: After meeting
Caesar's conspirators he reconciled in a friendly
manner and expressed his grief over Caesar's death.
Deceitfully he turned tables on the conspirators through
his funeral speech.
Great Orator: Due to his good oratory skills, he
mobilized the mob against the conspirators.
Q7: Read the extract and complete the
statements that follow:
But I am constant as the northern star,
Of whose true-fix'd and resting quality
There was no fellow in the firmament.
(i) The speaker of these lines is _________________
(a) Julius Caesar
(b) Cassius
(c) Octavius Caesar
(d) Brutus
(ii) The northern star is also known as .
(a) Venus
(b) Pole star
(c) Mercury
(d) Jupiter
(iii) Literary device used in the above lines is .
(a) simile
(b) metaphor
(c) personification
(d) alliteration
Answer:
(i) (a) Julius Caesar
(ii) (b) Pole star
(iii) (a) simile
Q8): Read the extract and complete the
statements that follow:
My credit now stands on such slippery ground,
That one of two bad ways you must conceit me,
Either a coward or a flatterer.
(i) Antony addresses to ___?
(a) Caesar
(b) Caesar's supporters
(c) conspirators
(d) mob
(ii) The word 'credit' in the above context means ______
___.
(a) reputation
(b) disrepute
(c) loan
(d) identity
(iii) The speaker refers to 'slippery ground' because .
(a) the ground was slippery.
(b) blood was flowing under his feet.
(c) his reputation was at stake.
(d) he may not win over the confidence of the listeners.
Answer:
(i) (c) conspirators
(ii) (a) reputation
(iii) (c) his reputation was at stake.
Q 9: Shakespeare used supernatural elements at
many occasions in the play? What are these
elements and what do they contribute to the play?
Answer: Shakespeare used supernatural elements in the
play to create an atmosphere of horror or to predict
something bad would happen. In Julius Caesar, these
elements are portents of evil predicting Caesar's death.
A few supernatural elements that came in the play are:
Upheaval in nature: A night before Caesar's murder,
there has been a a great upheaval in nature.
Calpurnia's nightmare: A bad dream seen by Caesar's
wife about his murder.
Watchman's dream : Blood rain in capital, lioness
giving birth to her cubs in the streets of Rome, cries of
dead and groaning of ghosts etc. were considered as
bad omen in the play.

CLASS X TWO GENTLEMEN OF VERONA Q/A

(Q & A)
Q1: What are the qualities of a gentleman?
Answer:
Self-Respect
Determined
Dignified
Compassionate
Well-mannered
Caring
Hard working
Q2:  Based on your reading of the story answer
the
following questions by ticking the correct
options.
(i) The driver did not approve of the narrator
buying fruit from the two boys because:
(a) the boys were untidy and poorly dressed
(b) the strawberries were not fresh
(c) they were asking for a heavy price
(d) the driver did not approve of small boys who
worked
Answer: (a) the boys were untidy and poorly dressed
(ii) The narrator was most impressed by the boys’:
(a) desire to earn money
(b) willingness to work
(c) ability to perform many tasks
(d) sense of fun
Answer: (c) ability to perform many tasks
(iii) Nicola was not pleased when Jacopo asked the
narrator to drive them to Poleta as he:
(a) did not want a stranger to become involved with
their plans
(b) preferred going to Poleta by train so that he could
enjoy the scenery
(c) did not want to ask anyone for favours
(d) did not want to take help from someone he did not
know well
Answer: (a) did not want a stranger to become involved
with their plans
(iv) The narrator did not go inside Lucia’s room as :
(a) he did not want to intrude into their privacy
(b) he thought that the boys would object
(c) Lucia would not welcome a stranger
(d) the boys would feel he was spying on them
Answer: (a) he did not want to intrude into their
privacy
(v) The boys were the first to join the resistance
movement against the Germans because :
(a) the Germans had hurt their sister
(b) the Germans ruled the city
(c) the Germans had ruined their family
(d) the Germans had destroyed their home
Answer: (d) the Germans had destroyed their home
(vi) The author did not speak to the boys on their
return journey because
(a) he thought the boys would prefer to keep their
secret
(b) he thought the boys were ashamed of their sister’s
condition
(c) he thought they won’t tell him the truth
(d) he thought the boys might ask him for money for
their sister.
Answer: (a) he thought the boys would prefer to keep
their secret
Q3: What do you understand by the following
statements
(a) "We do many things,sir,"Nicola answered
seriously. He glanced at us hopefully.
Answer: The above statement means that both Nicola
and Jacopo were trying very hard to earn their
living. At the same time they were expecting that the
narrator also would ask for their services,
so that they could earn some money.
(b) He coloured deeply under his sunburn,then grew
pale.
Answer: The statement shows that the boys were shy.
Nicola felt embarressed when the narrator enquired
about their earnings and what they do with the money.
He was not used to such questions. Therefore, he grew
pale.
(c) He smiled uncomfortably."Just plans,sir," he
answered in a low voice.
Answer: Nicola felt uneasy when the narrator asked
whether they had plans to emigrate to the States.
He was evasive and do not want to share their
sufferings with anyone.
(d) Yet in both these boyish faces there was a
seriousness which was far beyond their years.
Answer: Although the boys were very small, but they
possess maturity in their understanding and work. They
were extremely hard-working, sincere and committed to
work. These qualities are very uncommon in children.
Q4: Why didn't Luigi, the driver,approve of the two
boys?
Answer: Luigi found both the boys shabby and uncouth.
They had tangled hair, dark earnest eyes,brown skin
and looked quiet ill-clad. They appeared to be pathetic.
Moreover he thought that they might sell fruits that are
not fresh.
Q5 Why were the narrator and his
companion impressed by the two boys?
Answer: They were very impressed by the boys because
they were highly committed and devoted towards work
at such a tender age. They were ready to do all sorts of
odd jobs to earn money. They
exhibited dedication,determination and sincerity while
working.
Q6: Why was the author surprised to see Nicola and
Jacopo working as shoeshine boys?
Answer: During his first meeting with Nicola and Jacopo,
the boys were selling fruits. Next time, they were
polishing shoes to earn money. So,it was a surprise for
him to see that at this tender age, they were ready to
do any type of work.
Q7: How were the boys useful to the author?
Answer: Nicola and Jacopo proved themselves useful. If
they want a pack of american cigrattes, seats for the
opera or the name of a good restaurant, Nicola and
Jacopo could be relied upon to satisfy their needs.
Q8: Why were the boys in the deserted square at
night? What character traits do they exhibit?
Answer: The boys were in the deserted square at night
because the last bus from Padua was expected to come
there at that time and they hoped to sell the bundle of
unsold newspapers to the passengers in
the bus. They exhibited extreme hardwork, dedication,
sincerity, determination, devotion towards work,
tolerance,tremendous self respect and dignity.
Q9: The narrator asks the boys," Must you work so
hard? You both look rather tired." The boys
reply,"We are not complaining,sir." What do you
learn about the boys from their reply?
Answer: From their reply we can make out that the
boys were highly commited and devoted towards work
at such a tender age.They had extreme patience,
endurance and tolerence. They were also extremely
hard-working.They were  non-complaining, rough and
tough children who wanted to maintain their dignity
and self-respect.
Q10: When the narrator asks the boys about their
plans, they were evasive.Why don't they disclose
their problems?
Answer: The boys don't disclose their problems to the
narrator when the latter ask them about their
plans because they do not want to loose their dignity
and self-respect by not asking anyone for
sympathy or financial help.
Q11): ‘When the resistance movement
began secretly to form they were among the first to
join. When the war was over and we had peace at
last, they came back to their beloved sister.’
(a) Who are the “they” referred to here?
(b) Why did they join the resistance movement?
(c) What had happened to their sister?
Answer : (a) Here ‘they’ refers to the two brothers,
Nicola and Jacopo.
(b) They joined the resistance movement because the
war waged by Germany had destroyed their family. It
had killed their father. Their house had been destroyed
and the war had separated them from their sister.
(c) Their sister, Lucia, who wanted to be a singer, had
tuberculosis of the spine due to cold and starvation.
Q12 Why didn’t the two boys disclose their
problems to the author?
Answer: Despite leading a destitute life, the boys didn't
disclose their problems to the author because they did
not want their private suffering be made public. They
would like to live with self-respect and had strong will
power to accept responsibility for their own lives.

CLASS X HUMAN EYE Q/A

Q1(NCERT): What is meant by power of
accommodation of the eye?
Answer: Power of accommodation is the ability
of the eye lens to focus near and far objects
clearly on the retina by adjusting its focal length.
Power of accommodation of the eye is limited. It
implies the focal length of the eye lens cannot be
reduced beyond certain minimum limit.
Q2(CBSE 2011): A person cannot see the
objects distinctly, when placed at a distance
less than 50 cm.
(a) Identify the defect of vision.
(b) Give two reasons for this defect.
(c) Calculate the power and nature of the lens he
should be using to see clearly the object placed at
a distance of 25 cm from his eyes.
(d) Draw the ray diagrams for the defective and the
corrected eye.
Answer: (a) Defect of vision = Hypermetropia  or Long-
sightedness
(b) Reasons for the defect are:
Curvature of lens or retina becomes less than normal
increases focal length.
Ciliary muscles become stiff
Shortening of eye ball due to which distance between
retina and and lens reduces and image is formed
beyond retina.
(c) Given, u = -25 cm, v = -50cm, f = ?
Applying lens formula,      1/f = 1/v - 1/u
⇒1/f = -1/50 - (-1/25) = -1/50 + 1/25 = (-1+2) /50 =
1/50
⇒ f = 50cm = 0.5m
∴ Power of the lens = 1/f = 1/0.5m = + 2D
∴ A convex lens having power of 2D can be used to
correct the vision.
(d) ray diagrams for the defective and the corrected
eye.
Q3(NCERT): A person with a myopic eye cannot see
objects beyond 1.2 m distinctly. What should be
the type of the corrective lens used to restore
proper vision?
Answer: The distance of far point x = 1.2m
To view distant objects, concave lens of focal length
-1.2 should be used.
i.e. f = -x = -1.2m
Power of lens = 1/f = 1/(-1.2m) = -0.83D
Q4(CBSE 2011): Name the part of the human eye
that helps in changing the focal length of the eye
lens.
Answer: Ciliary muscles.
(Note: Pupil regulates and controls the amount of light
entering the eye.)
Q5(NCERT MCQ): The human eye can focus objects
at different distances by adjusting the focal length
of the eye lens. This is due to
(a) presbyopia.
(b) accommodation.
(c) near-sightedness.
(d) far-sightedness.
Answer: (b) accommodation.
Q6(NCERT MCQ): The human eye forms the image
of an object at its
(a) cornea.
(b) iris.
(c) pupil.
(d) retina.
Answer: (d) retina.
Q7(NCERT MCQ): The least distance of distinct
vision for a young adult with normal vision is about
(a) 25 m.
(b) 2.5 cm.
(c) 25 cm.
(d) 2.5 m.
Answer: 25cm
Q8(NCERT MCQ): The change in focal length of an
eye lens is caused by the action of the
(a) pupil.
(b) retina.
(c) ciliary muscles.
(d) iris.
Answer: (c) ciliary muscles.
Q9(NCERT): What is the far point and near point of
the human eye with normal vision?
Answer: The near point of the eye is the minimum
distance of the object from the eye, which
can be seen clearly. For a normal human eye, this
distance is 25cm .
The far point of the eye is the maximum distance upto
which the eye can see the objects clearly without strain.
The far point of the normal human eye is infinity.
Q10(CBSE 2011): A boy uses spectacles of focal
length – 60 cm. Name the defect of vision he is
suffering from. Which lens is used for the
correction of this defect? Compute the power of
this lens.
Answer: Given f = -60 cm =-0.60m
The -ve sign of focal length indicates that the lens is
concave.  ∴ the boy suffers from myopic (short
sightedness) vision.
Power of the lens = 1/f(in m) = 1/(-0.60) = -1.67 D
Q11(NCERT): A student has difficulty reading the
blackboard while sitting in the last row. What could
be the defect the child is suffering from? How can
it be corrected?
Answer: The student has difficulty in seeing distant
objects. He might be suffering from myopia. The defect
can be corrected using a concave lens of appropriate
focal length.
Q12(CBSE): Why do we have two eyes instead of
one?
Answer: Having two eyes instead of one is advantageous
for the following:
field of view is more with two eyes than one eye.
two eyes gives us three dimensional vision (stereo
vision) of an object.
Q13(NCERT): A person needs a lens of power –5.5
dioptres for correcting his distant vision. For
correcting his near vision he needs a lens of power
+1.5 dioptre. What is the focal length of the lens
required for correcting (i) distant vision, and (ii)
near vision?
Answer:
(i) Distant vision:  Given focal length (f) = ?, Power (P) =
-5.5D
P = 1/f ⇒ f = 1/P = 1/(-5.5)m = -100/55cm = -18.2
cm
(ii) For near vision, P = +1.5 D
⇒ f = 1/P = 1/1.5m = 1000/15cm = 66.7 cm
Q14(CBSE 2012): Define dispersion of white light
and name the colours of white light in order?
Answer: The splitting of light into its component colours
is called dispersion. White light splits into seven colours
(VIBGYOR) i.e. violet, indigo, blue, green, yellow, orange
and red. Isaac Newton was the first to use a glass prism
to obtain the spectrum of sunlight.
Q15(NCERT): The far point of a myopic person is 80
cm in front of the eye. What is the nature and
power of the lens required to correct the problem?
Answer: Given, distance of far point (x) = 80 cm, P = ?
To view distant objects correctly, focal length of the
corrective lens = f = -x = -80cm
Power of the lens (P = 1/(f in metres) = 1/(-0.80) =
100/-80 = -1.25D
The lens is concave of powed -1.25D
Q16(NCERT): Make a diagram to show how
hypermetropia is corrected. The near point of a
hypermetropic eye is 1 m. What is the power of the
lens required to correct this defect? Assume that
the near point of the normal eye is 25 cm.
Answer: For diagram see question 2(b) above.
Given v = -1m = -100cm
u = -25cm
Using lens formula, 1/v -/1u = 1/f
⇒ -1/100 + 1/25 = 1/f
⇒ f = 33.3 cm  - 0.333m
Power of the lens = 1/f = 100/33.3 = 3D
Q17(NCERT): Why is a normal eye not able to see
clearly the objects placed closer than 25 cm?
Answer: Since the focal length of eye lens cannot be
decreased beyond certain minimum length.
Q18(Old CBSE Curr. 2006): List four common
defects which can be corrected with the use of
spectacles.
Answer: Four common defects that can be corrected by
using spectacles:
1. Hypermetropia
2. Myopia
3. Astigmatism
4. Presbyopia
Q19(NCERT): What happens to the image distance
in the eye when we increase the distance of an
object from the eye?
Answer: The size of the eye can change, so the image
distance is fixed. When we increase the distance of an
object from the eye, the image distance in the eye does
not change. Due to power of accommodation of the
eye, focal length of the eye lens is changed which
compensates the increase in object distance. Hence
image distance remains fixed and image is formed on
the retina of the eye.
Q20(NCERT): Why do stars twinkle?
OR
Q(CBSE 2012): Explain why do stars twinkle and
planets do not?
Answer: The twinkling of a star is
due to the earth's atmospheric
refraction. The earth's atmosphere
is moving and it consists of
pockets of warm and cold air. Thus
the atmosphere has variations in
refractive indices of air. Stars are
very far away from the earth and
emit their own light. Being very far
from the earth, these are
considered point sources. When a
star light enters the earth's
atmosphere, it undergoes multiple
refractions and bends
continuously towards the normal
till it enters our eyes. Its apparent
position appears higher than the
normal one. Due to mobility of air
and variation is temperature, this
apparent position of star is not
steady and moves continuously giving a twinkling effect.
When in space (outside the earth's atmosphere) stars
do not appear twinkle. Planets as compared to stars are
closer to the earth and appear bigger (we cannot
consider them point sized like stars). It nullifies the
twinkling effect.
Q21(NCERT): Explain why the planets do not
twinkle.
Answer: The distanced between planets and the earth is
less as compared to stars. Planets cannot be considered
as point sources. The apparent shift in their position
due to their position cannot be observed because they
subtend greater angle at the eye. Comparatively larger
size, their brightness do not change and do not give
twinkle effect.
Q22: What is Mirage? How does it occur?
Answer: A mirage is an optical illusion which is generally
observed in deserts or over hot surfaces like a coal
tarred road during hot summers. In summers, the layer
near to earth surface is hotter and lighter than upper
layers of the air. Due to variation of optical densities of
air layers, light from an object (e.g. tree) undergoes
series of internal reflections and bend upwards. It gives
an inverted virtual image below the seen object. To a
distant traveller it gives shinning water effect called
mirage.
Q23: What are the causes of myopia?
Answer: Causes of myopia are:
Increase in the length of the eye ball leads to increase in
distance of the retina from the eye.
Decrease in focal length of eye lens.
Q24: What is Tyndall effect?
Answer: The scattering of light by colloidal particles is
called Tyndall effect. When a beam of light strikes the
minute particles of earth’s atmosphere which are
suspended particles of dust and molecule of air the path
of beam become visible. The phenomenon of scattering
of light by the colloidal particle is called Tyndall Effect.
It can be observed when sunlight passes through a
canopy of a dense forest.
Q25: How does colour of scattered light depend on
colloidal particles?
Answer: The colour of the scattered light depends on
the size of the scattering particles

CLASS X LIGHT REFLECTION AND REFRACTION

Q1 : In which type of lens linear magnification is always
less then one?
Answer: Concave Lens always has linear magnification
less than one, because it always gives diminished
images.
Q2 : John obtained a magnification of 1 with concave
mirror of focal length 10cm. What is the object distance
from mirror?
Answer: m = 1. Therefore u = v. Apply it in mirror
formula, you will get v = 20 cm.
Q3 : Which mirror has a wider field of view?
Answer: convex mirrors have wilder field view, that's
why these are used as rear view-mirrors in vehicles.
Q4 : Which is optically denser out of the two mediums
M1 and M2 having n = 1.71 and 1.36
respectively.
Answer: M1 (it has higher value of refractive index).
Q5: Identify a mirror having focal length –15cm
Answer: concave mirror (see -ve sign of focal length).
Q6 : Why does a ray change its path when it passes from
one medium to another medium?
Answer: Because of refractive property of light.
Q7 : When a ray of light entering from air is incident on
the surface of a glass slab at an angle
of 90°, what will be the measure of angle of refraction?
Answer: It will be zero degree.
Q8 : Due to which property of light, sharp shadows of
opaque objects are obtained?
Answer: Since light travels in straight lines, any obstacle
obstructing the path will cast its shadow.
Q9 : Two medium with refractive index 1.31 and 1.50
are given. In which case
(i) Bending of light is more (ii)
speed of light is more
Answer: (i) 1.50 and ii) 1.31
Q10 : Why does the coin placed at the bottom of a
container appears to be raised when the
container is filled slowly with water?
Answer: Light ray emerging from water medium to air
medium bends away and then reaches the eye.
Q11: Under what circumstances there won’t be any
refraction of light when it enters from one
medium to another?
Answer: There are two possible cases:
(i) When light incidents at 90 degress (normal) it will
not bend.
(ii) Only applicable when light passes from optical
denser medium to rarer medium, if it is incident at an
angle greater than critical angle, it will reflect (called
internal reflection) but not refract.
Q12 : Can a plane mirror ever form a real image?
Answer: Real image can only be formed when the
reflected rays converge. As such for plane mirrors it is
not possible.  However, if the reflected yas are
converged (or appears converged), it can form real
image. Consider a source of light is at infinity (say sun),
and plane mirror is very small in size, its reflected image
will show a circular bright spot (image of the sun) on
the screen.
Q13 : What feature of light corresponds (analogous) to
loudness of sound?
Answer: Brightness
Q14 Identify types of mirror without touching.
Answer: Move mirror to and fro.
Plane Mirror: Mirror image is of true size.
Concave Mirror: Image is curved. Bringing the mirror
closer, magnifies the image. Moving it away, image is
inverted and reduced.
Convex Mirror: Mirror image is always diminished but
erect. The viewpoint is wider.
Q15: What is the focal length of a plane mirror?
Answer: Infinity
Q16: Will the reflected rays converge at point when
a parallel beam of light is incident on a concave
mirror?
Answer: Yes it will converge at the focal point of
concave mirror.
Q17: Name any use of Concave lens.
Answer: Concave lens are mainly used in spectacles for
the correction of shortsightedness.
Q19: Name the type of mirror which always forms
virtual and diminished  image.
Answer: convex mirror.
Q20: What is the angle of reflection if a ray falls
normally on a plane mirror?
Answer: Zero
Q21: A ray of light travelling in air enters obliquely
into water. Does the light ray bend towards the
normal or away from the normal. Why?
Answer: When a ray of light travelling in air enters
obliquely into water, it bends towards the normal. It
happens because water is optically denser than air.
Speed of light will also decrease.
Q22: What are the uses of convex mirror?
Answer:
rear-view mirror
reflector of street light
shopping malls and buildings have long paths have
convex mirrors around the corner
Q23: List the uses of concave mirror?
Answer:
shaving mirror
reflector in automobile lights and torches
by dentists to see back side of tooth
reflector of solar furnaces
Q24: How many images are formed for a point
source kept in between two plane mirrors M1 and
M2 at right angles to each other?
Answer: Three.
Q25: What shall be the direction of the incident ray
which after reflection from a spherical mirror
retraces its path?
Answer: In this case incident ray is directed towards the
centre of curvature.
Q26: What are the characteristics of the image
formed on a plane mirror?
Answer: Characteristics of Image formed on plane
mirror are:
1. Image is upright and is of same size as the object.
2. It is virtual
3. Laterally inverted

CLASS X PERIODIC CLASSIFICATION OF ELEMENTS

Q1: What are the defects in Modern Periodic
Table?
Answer: Following are the defects:
Position of hydrogen still dicey. It is not fixed till now.
Position of lanthanides and actinides has not been given
inside the main body of periodic table.
It does not reflect the exact distribution of electrons of
some of transition and inner transition
elements.
Q2: What are the salient features of Modern
Periodic Table?
Answer:
In a period of the periodic table, the number of valence
electrons increases as atomic number increases. As a
result, elements change from metal to metalloid to
nonmetal to noble gas.
Atomic size is a periodic property. As atomic number
increases in a period, atomic radius
decreases. As atomic number increases in a group,
atomic radius increases.
Positive ions have smaller atomic radii than the neutral
atoms from which they derive. Negative ions have larger
atomic radii than their neutral atoms.
Positive ions in the same group increase in size down
the group.
In a group, each element has the same number of
valence electrons. As a result, the elements
in a group show similar chemical behavior.
Metallic character decreases from left to right in a
period because of the increase in the
effective nuclear charge.
Non-metallic character increase from left to right in a
period because of ncrease in
effective nuclear charge.Non-metallic character
decreases down the group because of increase in the
size of the
atom.
Q3: Two elements X and Y have atomic numbers 12
and 16 respectively. Write the electronic
configuration for these elements. To which period
of the modern periodic table do these two
elements belong? What type of bond will be formed
between them and why?
Answer: Electronic configuration of X (Z=12): 2, 8, 2
Electronic configuration of Y (Z=16): 2, 8, 6
Both these elements belong to third period. An ionic
bond is formed between X and Y due to transfer of two
electrons from X to Y.
Q4: The present classification of elements is based
on which fundamental property of elements?
Answer: Atomic Number is the basis.
Q5: Li, Na and K are the elements of a Dobereiners
Triad. If atomic mass of Li is 7 and that of K is 39.
What would be the atomic mass of Na?
Answer: According of Dobereiner’s law of triads, the
atomic mass of the middle element, in this case Na,
should be the arithmetic mean of Li and K.
Thus,
arithmetic mean of Li and K = (7 + 39)/2    = 23
(Answer)
Q6: Define Dobereiner’s law of triads.
Answer: It states, "when elements are placed in order
of the ascending order of atomic masses, groups of
three elements having similar properties are obtained.
The atomic mass of the middle element of the triad is
equal to the mean of the atomic masses of the other
two elements of the triad."
Q7: Why did Dobereiner's system of classification
fail?
Answer:
Major drawback of Deberneir’s classification was that it
was valid only for a few groups of elements known
during that time. He was able to identify three triads
only.
Also with more accurate measurements of atomic
masses showed that the mid element of the triad did
not really have the mean value of the sum of the other
two elements of the triad.
For elements of very low mass or very high mass, the
law did not hold good. For example Flourine(F),
Chlorine (Cl), Bromine(Br). Atomic mass of Cl is not an
arithmetic mean of atomic masses of F and Br
Q8: Explain about position of metalloids in modern
periodic table.
Answer : In the Modern Periodic Table, a zig-zag line
separates metals from non-metals. The borderline
elements – boron, silicon, germanium, arsenic,
antimony, tellurium and polonium – are intermediate in
properties and are called metalloids or semi-metals.
Q9: Why does Silicon classified as metalloid?
Answer: Silicon is classified as a semi-metal or metalloid
because it exhibits some properties of both metals and
non-metals.
Q10: State Newland's law of octaves.
Answer: Elements are arranged in increasing order of
their atomic masses such that the properties of the
eighth element is repetition of the properties of first
element ( similar to eighth note  in an octave of music)
Q11: X and Y are the two elements having similar
properties which obey Newlands law of octaves.
How many elements are there in between X and Y?
Answer: The law states there are eight elements in an
octave (row). No. of elements between X and Y is six.
Q12: What are the drawbacks of Newland's law of
octaves?
Answer: Following are the major drawbacks:
1. Worked well with lighter elements (upto Calcium). After
that elements in eighth column did not possess
properties similar to element in first column.
2. Newland assumed only 56 elements existed so far. Later
new elements were discovered which did not fit into
octaves table.
3. Newland adjusted few elements in a same slot though
their properties were quite different. E.g. Cobalt and
nickel are in the same slot and these are placed in the
same column as fluorine, chlorine and bromine which
have very different properties than these elements. Iron,
which resembles cobalt and nickel in properties, has
been placed far away from these elements.
Q13: What periodic trends  do we observe in terms
of atomic radii or atomic sizes in Modern periodic
table?
Answer: Following two trends are observed.
1. Within each column (group), atomic radius tends to
increase from top to bottom. This trend results
primarily from the increase in the number of the outer
electrons. As we go down a column, the outer electrons
have a greater probability of being farther from the
nucleus, causing the atom to increase in size.
2. Within each row (period), atomic radius tends to
decrease from left to right. The major factor influencing
this trend is the increase in the nuclear charge as we
move across a row. The increasing effective nuclear
charge steadily draws the valence electrons closer to
the nucleus, causing the atomic radius to decrease.
Q14: Name the scientist who proposed modern
periodic law? On which fundamental property of
elements it is based?
Answer: Henry Moseley . He proposed atomic number
should be chosen as fundamental property (instead of
atomic mass) to classify elements.
Q15: On what basis did Mendeleev arrange the
elements?
Answer: On the basis of atomic masses.
Q16 : An element R of atomic number 12 combines
separately with NO 3- and (SO 4 )2- , (PO 4 )3- radicals.
a) Write the electronic configuration of element R
b) Write the formulae of the three compounds so
formed.
c) To which group of the periodic table does the
element ‘R’ belong?
d) Does it form covalent or ionic compound? Why?
Answer:
a) Electronic configuration of R is 2,8,2.
b) Compounds formed are: R(NO 3 )2 , R(SO 4 ) and R
(PO4 ) 2
c) R has two valence electrons and hence it belongs to
second group.
d) It forms ionic compound by loosing two electrons to
attain stable electronic configuration.
Q17 Why do you think the noble gases are
placed in a separate group?
Answer: Due to following reasons:
1. Similar inert behaviour
2. Similar electronic configuration
3. Available in low concentration.
Q18  Besides gallium, which other
elements have since been discovered that were left
by Mendeléev in his Periodic Table? (any two)
Answer: Scandium (Sc) and Germanium(Ge)

CLASS X CARBON AND ITS COMPOUNDS

Q1 . What is next homologue of C3 H 7 OH is called?
Answer: The next homologue of C 3 H 7OH is called
butanol C 4H 9 OH.

Q2 . What is the molecular formula of the alcohol
which can be derived from propane?
Answer: Propane: CH 3 -CH2 -CH 3 or C 3 H8
Alcohol obtained from propane is C 3 H 7OH.

Q3 . What is meant by the term functional group?
Answer: An atom or a group of atoms, which makes a
carbon compound reactive and decides its
properties. is called a functional group.

Q4 . Give the names of the functional groups: (CBSE
2007)
i) -CHO (ii -C=O
Answer: (i) Aldehydic group (ii) Ketonic group.

Q5 . Give the names of the following functional
groups: (CBSE 2007)
i) —OH (ii) —COOH
Answer: (i) Alcoholic (ii) Carhoxylic.

Q6 . Which functional groups always occur at the
terminal position of a carbon chain?
Answer: Aldehydic group R—CHO (R is tue alkyl group),
and
Carboxyl group   R—COOH (R is the alkyl group).

Q7 . Why a candle flame burns yellow, while a
highly-oxygenated gas-fuel flame burns blue?
Answer: The most important factor determining color of
the flame is oxygen supply and the extent of fuel-
oxygen pre-mixing, which determines the rate of
combustion and thus the temperature and reaction
paths, thereby producing different color hues. In case
of candle, it is an incomplete combustion and the flame
temperature is not high. This gives a yellow flame. While
a highly-oxygenated gas (e.g. ethyne) flame burns blue
because of complete combustion raising a very high
temperature.

Q8 . Why is the reaction between methane and
chlorine considered a substitution reaction? [CBSE
2008]
Answer: Methane reacts with chlorine in the presence of
sunlight to form chloromethane and hydrogen chloride.
CH4 + Cl 2 → CH3 Cl + HCl
With the excess of chlorine, aH the four hydrogen
atoms of methane are replaced by chlorine atoms to
form carbon tetrachloride (CCl 4). This reaction is
considered as substitution reactions because hydrogen
of methane is substituted by chlorine.

Q9 : Why does Carbon form compounds mainly by
covalent bonding?
Answer. Being tetravalent carbon atom, it is neither
capable of losing all of its four valance electrons nor it
can easily accept four electrons to complete its octet.
Both of these are requirements of ionic bond formation
and are energetically less favourable. Carbon completes
its octet by sharing of electrons and hence covalent
bonding is preferred.

Q10 . Give a chemical test to distinguish between
saturated and unsaturated hydrocarbons.
Answer. When saturated compounds are burnt in air,
they give a clear (blue) flame but the burning of
unsaturated compounds (akenes and alkynes) gives a
sooty (yellowish) flame. Actually, saturated compounds
contain comparatively less percentage of carbon which
get completely oxidized by the oxygen present in air. On
the other hand, the percentage of carbon in
unsaturated compounds is more and it requires more
oxygen to get completely oxidized that is not fulfilled by
air. So due to incomplete oxidation they burn with a
sooty flame.
Bromine-water test: Br2 water is a brown coloured
liquid.
(a) Unsaturated hydrocarbons give addition reaction
with Br2 . So the colour of Br2-water gets decolourized.
R-C=C-R + Br2 →R-BrC-CBr-R
(b) Saturated hydrocarbons do not react with Br2 -
water, so the colour of Br2 .-water does not get
decolourised.

Q11 : What do you mean by Octane Rating?
Answer: Gasolines are rated on a scale known as octane
rating, which is based on the way they burn in an
engine. The higher the octane rating, the greater the
percentage of complex-structured hydrocarbons that
are present in the mixture, the more uniformly the
gasoline burns, and the less knocking there is in the
automobile engine. Thus, a gasoline rated 92 octane will
burn more smoothly than one rated 87 octane.

Q12 : Two compounds A and B react with each
other in the presence of a dehydrating agent to
produce an ester. Both react with Na to evolve
hydrogen gas. On reaction with Na 2 CO3 only A
evolves CO2 . Identify the functional groups present
in A and B giving reason for your answer.
Answer: Compound A contains –COOH group while
compound B contains –OH group.
Since carboxylic acids and alcohols react with each
other to form an ester, out of A and B, one is an
alcohol and the other is a carboxylic acid. This is
further strengthened by reaction of both with Na to
evolve hydrogen gas.
Only carboxylic acids react with Na 2 CO3 to evolve
CO2 , A contains –COOH group while B contains –OH
group.
Following video posted on You tube by tutor vista nicely
summarizes this chapter:

Q13 : An organic compound 'X' is widely used as a
preservative in pickles and has a molecular formula
C2 H 2 O2 . This compound reacts with ethanol to
form a sweet smelling compound ‘Y'.
a. Identify the compound ‘X’
b. Write the chemical equation for its reaction with
ethanol to form compound ‘Y’.
c. How can we get compound ‘X’ back from ‘Y’?
d. Name the process and write corresponding
chemical equation.
   e. Which gas is produced when compound ‘X’ reacts
with washing soda? Write the chemical equation.
Answer:
a. Compound X is ethanoic acid which gives and ester
(Y) when reacts with ethanol.
b. CH3 COOH + CH 3CH 2OH → CH3 COOC 2H 5
c. Esters gives back alcohol and carboxylic acid in the
presence of acid or base.
d. CH3 COOC 2 H5 ---NaOH → C 2 H5 OH + CH3 COOH
e.CO 2 gas is released.
CH 3COOH + Na2CO 3 → 2CH 3COONa + H 2 O +
CO2

Q14 What would be the electron dot
structure of carbon dioxide which has the formula
CO2 ?
Answer: Electron dot structure of CO 2 is O=C=O given in pic

Q16 How many structural isomers can you
draw for pentane?
Answer: There are three structural isomers of pentane:
(i) Pentane
CH3 ‒ CH2 ‒ CH2 ‒ CH2 ‒ CH3
(ii) 2-methyl Butane (iso-pentane)
CH3 ‒CH 2 ‒CH‒CH 3
|
CH3
(iii) 2-2 dimethyl propane (neo-pentane)
CH 3
|
CH3 ‒ CH ‒ CH 3
|
CH3

Q17) : What are the two properties of
carbon which lead to the huge number of carbon
compounds we see around us?
Answer: Two properties of carbon that attributes to its
large family of carbon compounds are:
1. Catenation: Ability to form chains with other atoms of
carbon by covalent bonding.
2. Tetravalency: Valency = 4 i.e. it forms four covalent
bonds with four other atoms.

Q18 : What is Covalent bonding?
Answer: The chemical bonding occurs due to mutual
sharing of electron pairs of two or more atoms of
different elements is called covalent bonding. By mutual
sharing of electron pairs atom attain noble gas
configuration. e.g. In Hydrogen molecule (H 2 ), the two
H-atoms combine by covalent bonding (H-H).

Q19 : What are Hydrocarbons? Give examples.
Answer: Compounds of carbon and hydrogen are called
hydrocarbons. Methane, Ethane, Butane, ethyne,
propene, benzene, petroleum products all are examples
of hydrocarbons.

Q20  What are saturated
hydrocarbons?
Answer: The hydrocarbons in which valency of carbon
is satisfied by a single covalent bond are called
saturated hydrocarbons. Alkanes like methane (CH 4 ),
ethane(C 2 H6 ), propane(C 3 H 8 ) etc. are examples of
saturated hydrocarbons. Saturated hydrocarbons will
generally give a clean flame.

Q21  "Saturated hydrocarbons burn
with a blue flame while unsaturated hydrocarbons
burn with a sooty flame". Why?
Answer: Saturated hydrocarbons have only C-C and C-H
single bonds and thus contain the maximum
possible number of hydrogen atoms per carbon atom.
With sufficient oxygen, saturated hydrocarbons burn
completely and give blue flame.
CH4 + 2O 2 → CO2 + 2H 2 O
Unsaturated hydrocarbons contain a carbon-carbon
double bond (C=C) or triple bond (C≡C). Hence they
contain less number of hydrogen than carbon.
Unsaturated hydrocarbons undergoe incomplete
combustion and give yellow flame along with black
sooty(carbon).
C 2H 4 + O 2 → CO 2 + 2H 2 O + C(s)

Q22 : What are isomers?
Answer: Compounds with identical molecular formula
but different structures are called structural isomers.
Organic compounds show a great level of isomerism.
Isomers may be structural (due to difference in
arrangement of C atoms forming chain) or stereo (due
to arrangement of bonds in chain). With increase in
number of carbon atoms in a molecular formula leads
to increase in number of isomers.
C‒C‒C‒C           OR       C-C-C
|
C
O
Q23 Why do ionic compounds have high
melting points?
Answer: Ions have strong electrostatic forces of
attraction among them forming ionic compounds. It
requires lot of energy to break these ionic bonds or
forces. That's why ionic bonds have high melting points.

Q24 : What are the characteristics of Homologue
series?
Answer: Important characteristics of Homologue series
are:
1. Have same general formula.
2. Belong to same functional group.
3. Have general methods of separation.
4. Have similar chemical properties.
5. Show similar gradation of physical properties. e.g.
boiling points of alcohol increase with increase in their
molecular weights.
6. Similarly solubility decreases with increase in molecular
weights.

Q25 : What is the general formula of Alkanes?
Answer: C nH 2n+2
Q26 : What is a hetroatom? What is the hetroatom in
alcohol functional group?
Answer: In a hydrocarbon chain, one or more
hydrogen atoms can be replaced by other atoms
according to their valencies. The element which
replaces hydrogen in the chain is called a heteroatom.
e.g. in  alcohol (-OH) functional group, oxygen is the
hetroatom.

CLASS X METALS & NONMETALS

Q & A
Q1: List any five physical properties of metals.
Answer: Physical properties of metals are:
1. Metals are usually hard (exceptions are:
sodium and potassium).
2. These are sonorous.
3. These are lustrous.
4. Metals exhibit malleability and ductility.
5. Mostly they are solids (exception is mercury)
6. They exhibit high tensile strength.
7. These have high densities.

Q2: Are metals electronegative or
electropositive?
Answer: Metals are electropositive i,e. they form
cations by loosing electrons.

Q3: Define Malleability.
Answer: Malleability is the property of a metal, by which
it can be beaten into thin sheets.

Q4: Name a metal which can be cut with a knife?
Answer: Sodium

Q5: Give examples of metals which are found in
liquid form at room temperature.
Answer: Mercury and Gallium

Q6: Define ductility. Give two examples of metals
that exhibit this property.
Answer: Ductility is the property of a metal by which it
can be drawn into thin wires. e.g. gold and silver.

Q7: Give an example of metal which is
i. the best conductor of heat
ii. the poor conductor of heat
Answer: (i) Silver  (ii) lead

Q8: What are metalloids? Give examples of
metalloids.
Answer: The elements that exhibit properties of both
metals and non – metals are called metalloids.
e.g. bismuth, silicon, germanium, arsenic, antimony,
tellurium and polonium

Q10: What are minerals?
Answer: The Inorganic elements or compounds of
various metals found in nature, associated with their
earthly impurities are called Minerals.

Q11: Can metals be extracted from all types of
minerals?
Answer: No. Some minerals may have high percentage
of metals while other do not.

Q12: What are ores?
Answer: Those minerals from which metals can be
extracted profitably and conveniently are called Ores.

Q13: Define metallurgy.
Answer: The process of extracting metals from their
ores followed by refining is known as metallurgy.

Q14: Give an example of non-metal which is
lustrous.
Answer: Iodine

Q15: Give an example of a non-metal which is hard
and has high melting point.
Answer: Diamond (allotrope of Carbon)

Q16: What is gangue and what is concentration?
Answer: Ores are usually associated with unwanted
earthly matter called gangue (sand, clay etc.,) and the
removal of this unwanted impurity is called
concentration. The gangue has to be removed before
the extraction of metals.

Q17:  Why do potato chips manufacturers fill the
packet of chips with nitrogen gas?
Answer: Nitrogen provides an inert atmosphere to
prevent chips from getting oxidised. Nitrogen is an
antioxidant which prevents oxidation of substances and
that's why such type of food material is flushed with
nitrogen in packs.

Q18: Name any non-metal which is found in liquid
state at room temperature.
Answer: Bromine

Q19 ): You are given two statements a and b,
select the correct inference from this:
a. Metals conduct heat.
b. Diamond is the best conductor of heat.
i. Hence diamond is a metal
ii. Statement a is correct
iii. Statements a and b is correct
iv. None of the above
Answer: ii. Statement a is correct

DIFFERENCE BW METAL AND NONMETAL

CLASS X ACID BASES SALTS Q/A


Q1: The most commonly used indicator in
laboratory is
(a) Methyl Orange
(b) Litmus
(c) Phenolphtalein
(d) Universal Indicator
Answer: Universal Indicator

Q2: Olfactory indicators are:
(a) Clove
(b) Turmeric
(c) Soap
(d) Rose Petals
Answer: (a) Clove

Q3: An element common to all acids is
(a) Chlorine
(b) Nitrogen
(c) Oxygen
(d) Hydrogen
Answer: (d) Hydrogen

Q4: Metal carbonate on reaction with dilute acid
release
(a) CO 2
(b) CO
(c) H 2 O
(d) H 2
Answer: (a) CO2

Q5 ln general, salts
(a) are ionic compounds
(b) contain hydrogen ions
(c) contain hydroxide ions
(d) turn litmus red
Answer: (a) are ionic compounds

Q6: On passing excess of CO 2 gas in an aqueous
solution of calcium carbonate, milkiness of the
solution
(a) persists
(b) fades
(c) deepens
(d) disappears
Answer: (b) fades

Q7 When magnesium and hydrochloric
acid react, they produce
(a) Oxygen and magnesium chloride
(b) Chlorine and magnesium oxide
(c) Hydrogen and magnesium chloride
(d) Hydrogen and magnesium oxide
Answer: (c) Hydrogen and magnesium chloride

Q8:  Dissolution of acid or base in water is
(a) Exothermic
(b) Endothermic
(c) Violent
(d) None of these
Answer: (a) Exothermic

Q9: Water contains more H+ ions than OH- ions. In
this case, water is
(a) neutral
(b) basic
(c) acidic
(d) cannot say.
Answer: (c) acidic

Q10: When an acid reacts with a base what
compounds are formed?
(a) water only
(b) metal oxides only
(c) a salt only
(d) a salt and water
Answer: (d) a salt and water

Q11: Which of the following is a property of an
acid?(a) slippery feel
(b) non-reactive
(c) sour taste
(d) strong color
Answer: (c) sour taste

Q12: On diluting an acid concentration of H+ per
unit volume
(a) increases
(b) decreases
(c) remains unaffected
(d) depends on type of acid used.
Answer: (b) decreases

Q13: What is pH?
(a) the positive logarithm of the hydroxide ion
concentration
(b) the positive logarithm of the hydrogen ion
concentration
(c) the negative logarithm of the hydroxide ion
concentration
(d) the negative logarithm of the hydrogen ion
concentration
Answer: (d) the negative logarithm of the hydrogen ion
concentration

Q14: Tartaric acid is the constituent of
(a) bleaching powder
(b) baking powder
(c) washing powder
(d) plaster of paris
Answer: (b) baking powder

Q15: A solution turns blue litmus red. Its pH value
is likely to be
(a) 4
(b) 7
(c) 9
(d) 12
Answer: (a) 4

Q16: What is the name of H 2SO 3 ?
(a) Sulphuric Acid
(b) Sulphurous Acid
(c) Sulphite Acid
(d) Hydrogen Sulphide.
Answer: (b) Sulphurous Acid

Q17: Which gas is produced by reaction of base
with metal ?
(a) Carbon dioxide
(b) Dioxygen
(c) Dihydrogen
(d) Dinitrogen
Answer: (c) Dihydrogen

Q18: Acid + Metal-oxide  → ?
(a) Base + Water
(b) Salt + Water
(c) Base + Salt
(d) Metal + Salt
Answer: (b) Salt + Water

Q19: Which of the following is a weak acid?
(a) Hydrochloric Acid
(b) Nitric Acid
(c) Acetic Acid
(d) Sulphuric Acid
Answer: (c) Acetic Acid

Q20: An indicator is what type of compound?
(a) reducing agent
(b) strong base or acid
(c) weak base or acid
(d) salt
Answer: (c) weak base or acid

Q21: Which of the following is strong acid ?
(a) Acetic acid
(b) Citric acid
(c) Nitric acid
(d) Oxalic acid
Answer: (c) Nitric acid

Q22: Name the organic acid present in tomato
(a) Tartaric Acid
(b) Malic Acid
(c) Lactic Acid
(d) Oxalic Acid
Answer: (d) Oxalic Acid

Q23: Fill in the blanks.
(a) Turmeric, clove, rose petals are ______ _____ .
(b) Acids ______ _______ bases to form ________ and
water.
(c) The term pH was coined by _______ .
(d) Turmeric turns _____ _______ in basic medium.
(e) ________ ________ is used in softening water.
(f) String acids show ______ ionisation while weak acids
show _______ ionisation.
(g) Calcium Sulphate hemihydrate is popularly known as
_____ ___ _____.
(h) Acids contain the hydrogen (H + ) as the only ______ _
______.
(i) Bases contain the Oxide (O 2- ) or hydroxide (OH -)
radical as the only _______ radical.
Answer:
(a) Olfactory indicators
(b) reacts with, salt
(c) Sørensen
(d) deep brown
(e) Washing Soda
(f) more, less
(g) Plaster of Paris
(h) positive radical
(i) negative

Q24: List the organic acid present in the following
objects:
(a) Citrus Fruits (lemon, orange)
(b) Sting of bees and ants
(c) Rancid butter
(d) Tamarind, grapes, apples
(e) Apples
(f) Gastric juice
(g) Vinegar
(h) Fats
(i) Urine
(j) Sour milk, curd
Answer:
(a) Citrus Fruits (lemon, orange): Citric acid
(b) Sting of bees and ants: Formic acid
(c) Rancid butter: Butryic acid
(d) Tamarind, grapes, apples : Tartaric acid
(e) Apples: Malic acid
(f) Gastric juice: Hydrochloric acid
(g) Vinegar: Acetic acid
(h) Fats: stearic Acid
(i) Urine: Uric Acid
(j) Sour milk, curd: Lactic acid

Q25: State true (✓) or false (✗ )
(a) Heat is evolved during ionisation.
(b) Solution of glucose in water produces ions.
(c) Dry ammonia has no effect on litmus paper.
(d) Higher is the concentration of H(aq), lower is the
pH value.
(e) The concentration of aqueous solutions of acid, base
and salt are generally expressed in molarity.
(f) pH of a solution can vary from 0-14.
(g) HC1 is a weak acid.
(h) NaOH is a strong base.
(i) Curd is alkaline in comparison to fresh milk.
(j) pH = + log10[(H 3 O -]
(k) Distilled water does not conduct electricity.
(l) Analgesics helps to relieve acidity.
Answer:
(a) Heat is evolved during ionisation. - True(✓)
(b) Solution of glucose in water produces ions. False (✗)
(c) Dry ammonia has no effect on litmus paper. (True)

(d) Higher is the concentration of H(aq), lower is the
pH value. True(✓)
(e) The concentration of aqueous solutions of acid, base
and salt are generally expressed in molarity.True(✓)
(f) pH of a solution can vary from 0-14. True(✓)
(g) HC1 is a weak acid. False (✗)
(h) NaOH is a strong base. True(✓)
(i) Curd is alkaline in comparison to fresh milk. False (✗)
(j) pH = + log10[(H 3 O -] False (✗)
(k) Distilled water does not conduct electricity. True(✓)
(l) Analgesics helps to relieve acidity. False (✗)

Q26: Identify which of the following chemical
formulas is acid, base or salt. Write their
corresponding chemical names also.
(a) HCl
(b) NaOH
(c) NaCl
(d) Ca(NO 3) 2
(e) Ca(OH) 2
(f) HNO3
(g) NH 4 OH
(h) (NH 4 )2 SO 4
(i) CuO
(j) H 2SO 4
(k) CuCO 3
(l) H 2CO 3
(m) MgO
(n) Mg3 (PO 4) 2
Answer:
(a) HCl - Hydrochloric Acid
(b) NaOH - Sodium Hydroxide - Base
(c) NaCl - Sodium Chloride - Salt
(d) Ca(NO 3) 2 - Calcium Nitrate - Salt
(e) Ca(OH) 2 - Calcium Hydroxide
(f) HNO3 - Nitric Acid
(g) NH 4 OH - Ammonium hydroxide - Base
(h) (NH 4 )2 SO 4 - Ammonium sulphate - Salt
(i) CuO - Copper Oxide
(j) H 2SO 4 - Sulphuric Acid
(k) CuCO 3 - Copper Carbonate
(l) H 2CO 3 - Carbonic acid
(m) MgO - Magnesium Oxide
(n) Mg3 (PO 4) 2 - Magnesium Phosphate

Q27: You have been provided with three test tubes.
One of them contains distilled water and the other
two contain an acidic solution and a basic solution,
respectively. If you are given only red litmus paper,
how will you identify the contents of each test
tube?
Answer: The colour of red litmus paper changes to blue
indicates that the chemical is a base. If there is no
change in colour, then it is either acidic or neutral. We
can easily identify a base.
1. Mark the three test tubes as A, B, and C.
2. Take a drop of the solution A and put it on the red
litmus paper. Repeat the same process iwth solution B
and C.
3. If any of them changes colour to blue, then it is a
base.And remaining two are acid and neutral.
4. Now take a drop from the identified base and mix it
with a drop taken from the remaining two solutions
separately.
5. Check the drops of the mixtures on red litmus paper.
6. If the colour of red litmus turns blue, then the second
solution is neutral. If it does not change colour, then
the second solution is acid. This is because acidic and
basic solutions neutralize each other.

Q28: Why should curd and sour substances not be
kept in brass and copper vessels?
Answer: Curd and sour substances are acidic by nature.
e.g. curd contains lactic acid. When these substances
are kept in metal containers like brass and copper,
metal react with acid and liberate hydrogen gas and
other harmful substances, which may spoil these
substances.

Q29: Why vinegar is used in pickling?
Answer: Vinegar contains an organic acid called acetic
acid (CH 3COOH) which prevents the growth of micro
organisms. Therefore it is used in pickling.

Q30: Why phenolphthalein is considered acid base
indicator?
Answer: It is because phenolphthalein turns pink in
basic solution whereas it remains unaffected in acid or
neutral solutions. It is able to differentiate between acid
(colouless) and base (pink colour).

Q31 Which gas is usually liberated when
an acid reacts with a metal? Illustrate with an
example. How will you test for the presence of this
gas?
Answer: Hydrogen gas is liberated when an acid reacts
with a metal.
Take few pieces of zinc (Zn) granules in a delivery tube.
Add 5ml of hydrochloric acid (HCl). White fumes will
rise. Pass the gas to a soap solution or collect it in a
balloon (as shown in the following video). The gas
collected is Hydrogen gas. Since H2 gas has lower
density as compared to air, the balloon will float in air.
Zn (s) + 2HCl (aq) → ZnCl2 (s) + H 2 (g)
You can test the evolved hydrogen gas by its burning
with a pop sound when a candle is brought near the
balloon (or soap bubbles).

Q32 Metal compound A reacts with dilute
hydrochloric acid to produce effervescence. The gas
evolved extinguishes a burning candle. Write a
balanced chemical equation for the reaction if one
of the compounds formed is calcium chloride.
Answer: Since CO2 gas is liberated and the salt obtain
has metal Ca, it implies the reactant metal compound
shall be a carbonate i.e. CaCO3
The chemical equation is:
CaCO3 (s) + 2HCl (aq)  →   CaCl 2 (s) + CO2 (g) +
H2 O (l)
Calcium Carbonate + Hydrochloric Acid  → Calcium
Chloride + Carbon Dioxide + Water

Q33 Why do HCl, HNO 3 , etc., show acidic
characters in aqueous solutions while solutions of
compounds like alcohol and glucose do not show
acidic character?
Answer: As aqueous solution, HCl and HNO 3 dissociate
into H + and Hydronium (H 3 O+ ) ions.
HCl (aq) → H + + Cl -
H + + H2 O → H 3O +
Although glucose and alcohol contain hydrogen, as
aqueous solution, they do not dissociate into ions and
do not exhibit acidic character.

Q34(NCERT): Why does an aqueous solution of an
acid conduct electricity?
Answer: The aqueous solution of an acid contains H +
and Hydronium (H 3O + ) ions. Since ions carry extra
charge and are able to conduct electricity.

Q35: Why should acids be handled with care?
Answer: Acids have burning effect on our skin. They are
corrosive to living beings. Proper care must be taken
while handling acids in laboratory.

Q36: Why does dry HCl gas not change the colour of
dry litmus paper
Answer: Dry HCl gas does not form H + ions. It does not
show its acidic character. When in the aqueous
solution, an acid ionizes to form H+ ions. In this case,
neither HCl is in an aqueous form nor the litmus paper
is wet, therefore, the colour of the litmus paper does
not change.

Q37: While diluting an acid, why is it recommended
that the acid should be added to water and not
water to the acid?
Answer: When diluting, the acid should always be added
slowly to water and in small amounts. Adding water to
an acid is an exothermic process, it can cause
uncontrolled boiling and splashing. That's why it is
recommended that the acid should be added to water
and not water to the acid.

Q38: What is an amphoteric substance?
Answer: A substance is said to be amphoteric if it can
behave either as an acid or as a
base. Water is the most common amphoteric substance.

Q39: On the basis of origin, how acids are
classified?
Answer: On the basis of origin, acids are classified as:
1. Organic acids
2. Inorganic or Mineral acids

Q40: What are organic acids? Give two examples
Answer: Acids obtained from living beings (plants and
animals) are called organic acid.
e.g. citric acid present in fruits like lemon, oxalic acid in
tomato etc.

Q41: What are mineral acids? Give two examples
Answer: In general acids obtained from minerals or
non-living things are called mineral or inorganic acids.
Examples are:
Sulphuric acid (H 2 SO4 )
Nitric Acid (HNO 3)

Q42: What is the chemical name of Bleaching
powder? How it is prepared? List its uses.
Answer:
Chemical Name of Bleaching Powder: Calcium
Oxychloride
Chemical Formula: CaOCl 2
Preparation: It is prepared by passing chlorine gas
through dry slaked lime.
Ca(OH) 2 + Cl 2 → CaOCl 2 + H 2O
Slaked Lime + Chlorine →  Bleaching Powder +
Water
Uses:
1. As bleaching agent in textile industry.
2. As disinfectant in water purification.
3. In paper industry to bleach wood pulp

Q43: Which acid is used in Cola to give it a biting
sharp taste?
Answer: Phosphoric acid.

Q44: What is gypsum?
Answer: Plaster of Paris reacts with water to give a hard
mass called gypsum.
(CaSO 4 )2 . H2 O (s) + 3 H 2O (l) →
2CaSO 4 .2H 2 O (s)
Plaster for Paris + Water     → Gypsum

Q45 Define Dilution.
Answer: Mixing an acid or base with water results in
decrease in the concentration of ions (H 3 O + /OH –) per
unit volume. Such a process is called dilution and the
acid or the base is said to be diluted.

Q46 Tooth enamel is one of the
hardest substance in our body. How does it undergo
damage due to the eating of chocolates and
sweets? What should we do to prevent it?
or
Q: Why does tooth decay start when the pH of the
mouth is lower than 5.5?
Answer: Tooth decay starts when the pH of the mouth
is lower than 5.5. Tooth enamel, made up of calcium
phosphate is the hardest substance in the body. It does
not dissolve in water, but is corroded when the pH in
the mouth is below 5.5. Bacteria present in the mouth
produce acids by degradation of sugar (due to
chocolates and sweets) and food particles remaining in
the mouth after eating. The best way to prevent this is
to clean the mouth after eating food.
Using toothpastes, which are generally basic, for
cleaning the teeth can neutralise the excess acid and
prevent tooth decay.