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Page No 209:

Question 1:

The troposphere is
(a) the layer of the atmosphere in which we live.
(b) the layer in which clouds are formed.
(c) the layer in which weather changes occur.
(d) all of the above.

Answer:

(d) all of the above
Troposphere is the layer of atmosphere up to 16 km above earth's surface. We live in this layer. Here, clouds are formed and weather changes occur.

Page No 209:

Question 2:

Which of these is not an inactive gas?
(a) argon
(b) helium
(c) krypton
(d) oxygen

Answer:

(d) oxygen
Oxygen is a reactive gas.

Page No 209:

Question 3:

Which of the following is not found in the atmosphere?
(a) oxygen
(b) hydrogen
(c) nitrogen
(d) carbon dioxide

Answer:

(b) hydrogen
Hydrogen does not exist in atmosphere.

Page No 209:

Question 4:

Where is the ozone layer found?
(a) troposphere
(b) thermosphere
(c) exosphere
(d) stratosphere

Answer:

(d) stratosphere
Ozone layer is formed in the stratosphere.

Page No 209:

Question 5:

The words in columns I and II have been matched. Which is the correct set of answers?

Column I Column II
A. oxygen i. photosynthesis
B. carbon dioxide ii. protection from UV rays
C. nitrogen iii. breathing
D. ozone iv. found in proteins

(a) A-iii; B-i; C-ii; D-iv
(b) A-iii; B-i; C-iv; D-ii
(c) A-i; B-iii; C-iv; D-ii
(d) A-i; B-iii; C-ii; D-iv

Answer:

(b) A-iii; B-i; C-iv; D-ii
We breath oxygen and plants use carbon dioxide for photosynthesis. Nitrogen is a part of proteins. Ozone protects from UV rays of sun.

Page No 209:

Question 6:

The gas that helps to break down food in our body and thus release energy is
(a) oxygen.
(b) carbon dioxide.
(c) hydrogen.
(d) nitrogen.

Answer:

(a) oxygen
Food gets oxidised in presence of oxygen to release energy.

Page No 209:

Question 7:

After a candle has stopped burning in a covered beaker. An ant that is placed inside the beaker and covered will die, because
(a) the temperature inside the beaker was too high.
(b) the candle gave off poisonous gases.
(c) there is no more oxygen for it to respire.
(d) there was too much moisture inside.

Answer:

(c) there is no more oxygen for it to respire.
Burning of candle in a covered beaker uses all the oxygen inside the beaker and no oxygen is left for the ant to breath.

Page No 209:

Question 8:

Ravi wanted to find out which part of his school was most polluted. He smeared Vaseline on cellophane paper pieces of the same size and kept them in four different places. His observations are shown below.
Figure

Which place in his school is the most polluted?
(a) playground
(b) classroom
(c) canteen
(d) library

Answer:

(c) canteen
The cellophane paper smeared with vaseline and kept in the canteen has maximum pollutants sticked to it. Therefore, canteen is most polluted area.

Page No 209:

Question 9:

Which of the following groups contains only substances which are pollutants?
(a) carbon monoxide, sulphur dioxide, smoke
(b) sulphur dioxide, oxygen, nitrogen
(c) carbon dioxide, nitrogen, argon
(d) carbon monoxide, sulphur dioxide, neon

Answer:

(a) carbon monoxide, sulphur dioxide, smoke
All of them are hazardous to health; therefore, they are pollutants.

Page No 209:

Question 10:

Unravel these jumbled sentences to find the one that is not a good method to prevent air pollution.
(a) vride ynlo nehw oyu stmu
(b) lkaw rtosh sidntacse
(c) ntalp orme eerst
(d) urnb riedd eavlse

Answer:

(d) urnb riedd eavlse
The sentence is "burn dried leaves". This is not a good method to prevent air pollution.



Page No 210:

Question 11:

Replace the following with a word or a phrase.
(a) air in motion
(b) the liquid used to test for carbon dioxide
(c) the layer of air surrounding the earth
(d) increase in the temperature of the earth's atmosphere
(e) harmful rays from the sun
(f) the amount of water vapour present in the air
(g) a poisonous gas given out from the exhaust pipes of cars.
(h) addition of harmful substances to the atmosphere

Answer:

(a) Wind refers to the air in motion.
(b) Lime water is the liquid used to test for carbon dioxide.
(c) Atmosphere is the layer of air surrounding the earth.
(d) Global warming is the increase in the temperature of the earth's atmosphere.
(e) UV rays are the harmful rays from the sun.
(f) Humidity is the amount of water vapour present in the air.
(g) Carbon monoxide is a poisonous gas given out from the exhaust pipes of cars.
(h) Air pollution is the addition of harmful substances to the atmosphere.

Page No 210:

Question 12:

Raghav dipped an empty bottle vertically in a trough of water as shown in picture 1. He found that water did not enter the bottle. However, when he tilted the bottle slightly, he found bubbles coming out as shown in picture 2.
Figure
(a) Why did water not enter the bottle at first?
(b) Explain what Raghav observed when he tilted the bottle.

Answer:

(a) Water was not able to enter the bottle at first because of the presence of air in it.

(b) When Raghav tilted the bottle, the air of the jar came out as bubbles and subsequently, water entered the bottle. Therefore, he observed the formation of bubbles.

Page No 210:

Question 13:

Describe an experiment to prove that air is needed for burning.

Answer:

Air is needed for burning. To prove this, fix a candle on the table, light it and then cover it with a transparent beaker. The candle will burn initially but after some time, it will stop burning. This is because oxygen was initially present and all of it was consumed by the burning candle. Thus, when no oxygen was present, the candle stopped burning. This shows that air having oxygen is needed for burning.

Page No 210:

Question 14:

When an object catches fire, you are advised to wrap a woollen blanket around it. Can you explain why? (Hint: Air is needed for burning.)

Answer:

When an object catches fire, we are advised to wrap a woollen blanket around it to cut the air supply. Air is needed for burning. On wrapping the blanket around the object, no air will be available to the object and it will stop burning.

Page No 210:

Question 15:

State whether the following statements are true or false.
(a) Air consists of a single substance.
(b) When water is poured into a glass, air is pushed out of the glass.
(c) Trees need oxygen for photosynthesis.
(d) When we exhale, we give out the carbon dioxide produced in the body.
(e) The amount of water vapour in the air is always the same.
(f) Nitrogen is required by plants to make proteins.
(g) Aircrafts fly in the ionosphere as there is less friction in this zone.
(h) One per cent of air contains carbon dioxide, argon, helium, argon and krypton-all of which are inert gases.
(i) LPG and CNG burn using oxygen gas and release carbon dioxide gas.
(j) Nitrogen in the air also helps in burning.

Answer:

(a) False. Air is a mixture of gases.

(b) True.

(c) False. Trees need carbon dioxide for photosynthesis.

(d) True.

(e) False. Water vapour in atmosphere keeps on changing.

(f) True.

(g) False. They fly in stratosphere.

(h) False. Carbon dioxide is not an inert gas.

(i) True.

(j) False. Oxygen helps in burning.

Page No 210:

Question 16:

Radhika performed an experiment and wrote a record of what she had done. Can you rewrite these sentences in the correct order to describe her work? Draw a picture of her experiment. Can you explain what she observed?
(a) I used my wrist watch to check how long each candle burned.
(b) In the lid of the first jar, I punched several small holes.
(c) With my older brother's help, I fixed one candle in each jar and lit them.
(d) I collected the following items: two identical jam jars with lids, two identical small candles, matches, a nail and a hammer.
(e) I left the second jar open.
(f) I wanted to compare the time for which the candles could burn in the two jars.
(g) The second candle continued to burn for a long time.
(h) The candle in the first jar went out first and the jar was filled with smoke.
(i) I closed the first jar with its own lid.

Answer:



Correct order of Radhika's work:
(d) I collected the following items: two identical jam jars with lids, two identical small candles, matches, a nail and a hammer.
(c) With my older brother's help, I fixed one candle in each jar and lit them.
(i) I closed the first jar with its own lid.
(b) In the lid of the first jar, I punched several small holes.
(e) I left the second jar open.
(f) I wanted to compare the time for which the candles could burn in the two jars.
(a) I used my wrist watch to check how long each candle burned.
(g) The second candle continued to burn for a long time.
(h) The candle in the first jar went out first and the jar was filled with smoke.

She observed that air is needed for burning.



Page No 211:

Question 17:

Match the items in column I to those in column II.

Column I Column II
a. moving air i. photosynthesis
b. layer in which we live ii. inert gas
c. stratosphere iii. water vapour
d. radon iv. protein
e. oxygen v. smoke and fog
f. carbon dioxide vi. ozone layer
g. exhaled air vii. combustion
h. humidity viii. wind
i. smog ix. increased carbon
dioxide
j. nitrogen x. troposhere

Answer:

 

Column I Column II
a. moving air viii. wind
b. layer in which we live x. troposphere
c. stratosphere vi. ozone layer
d. radon ii. inert gas
e. oxygen vii. combustion
f. carbon dioxide i. photosynthesis
g. exhaled air ix. increased carbon dioxide
h. humidity iii. water vapour
i. smog v. smoke and fog
j. nitrogen iv. proteins

Page No 211:

Question 18:

Name the five layers of the atmosphere. Write a short note on the layer in which we live.

Answer:

The layers of atmosphere are troposphere, stratosphere, mesosphere, thermosphere and ionosphere.
We live in troposphere. It is 16 km thick. Movement of winds, formation of clouds and all the changes in weather take place in this layer.

Page No 211:

Question 19:

List some uses of oxygen.

Answer:

Oxygen is essential for living. We breath oxygen. It is needed for burning and also required for the release of energy from the food we eat.

Page No 211:

Question 20:

When you water the plants in a pot, you see bubbles on the surface of the soil. Can you explain this observation?

Answer:

Soil particles have air spaces in between them. When water is poured in the plants in a pot, water replaces the air present in soil particles. This escape of air is seen as bubbles on the surface of soil.

Page No 211:

Question 21:

You must have seen this sign displayed in many public places.
(a) Why are such signs put up?
(b) Name two place where you think it is necessary to put up such signs?
Figure

Answer:

(a) Such signs are put up to prevent air pollution by smoking.

(b) In hospitals and schools, it is necessary to put up such signs.



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