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Question 1:, , What is the composition of air?, , ANSWER:, , Air is a mixture of 79% nitrogen, 20% oxygen, 1%, carbon dioxide, water vapours and some other, gases. Air also contains dust particles., , Page No 153:, , Question 2:, , Which gas in the atmosphere is essential for, respiration?, , ANSWER:, , Oxygen is essential for respiration.

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Question 3:, , How will you prove that air supports burning?, , ANSWER:, , Take a candle. Place it in a tub. Light the candle, and also fill the tub with some water. Cover the, candle with an inverted glass. You will find that, the candle blows out after burning for some, time, and the water level inside the inverted, glass rises up to some extent., , , , The component, oxygen, of air inside the glass is, used up in burning. Therefore, water occupies, that space. This shows that air supports, , burning.

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Page No 153:, , Question 4:, , How will you show that air is dissolved in water?, , ANSWER:, , To show that air is dissolved in water we take, water in a pan and heat it. Just before it boils,, you will notice some bubbles at the inner surface, of the pan. These bubbles are formed because, of air dissolved in water., , Page No 153:, , Question 5:, , Why does a lump of cotton wool shrink in water?, , ANSWER:, , A lump of cotton wool shrinks when immersed in, water. This is because air present in the cotton, wool escapes. Thus, the volume of the cotton, wool decreases.