Q.1. What is the composition of air?
Ans. Air comprises of water vapour, Oxygen, Nitrogen, Carbon dioxide, dust and smoke.
Q.2. Which gas in the atmosphere is essential for respiration?
Ans. Oxygen gas in the atmosphere is essential for respiration.
Q.3. How will you prove that air supports burning?
Ans. To prove that air supports burning, let's take two lighted candles.
(i) Put one candle in a tumbler containing water and cover it with an inverted glass.
(ii) Put the second candle in open air. After some time, this covered candle gets extinguished and the water level rises up in the glass.
(iii) This happens because oxygen present inside the air in the glass was used up completely.
This experiment shows that air is necessary for burning.
Practical life example: In villages, the food is cooked on chulha. In the chulha , blowing air helps in quickly burning the wood in it. This also shows that air supports burning.
Q.4. How will you show that air is dissolved in water?
Ans. Take some water in a glass vessel or beaker. Heat it slowly on a tripod stand. Look carefully at the inner surface of the vessel, before reaching its boiling point, the bubble of air start rising from bottom to surface. These bubbles come from the air dissolved in water.
Q.5. Why does a lump of cotton wool shrink in water?
Ans. Sufficient volume of air is present in the cotton wool. When dipped in water, this air is replaced by less volume of water, so it shrink in water.
Q.6. The layer of air around the earth is known as _______.
Ans. The layer of air around the earth is known as the atmosphere.
Q.7. The component of air used by green plants to make their food, is _______.
Ans. The component of air used by green plants to make their food, is carbon dioxide.
Q.8. List five activities that are possible due to the presence of air.
(i) Living beings use air for respiration.
(ii) Plants use air (carbon dioxide) to prepare their food.
(iii) Blowing air (wind) is used for power generation by windmills.
(iv) Air helps in burning of fuels and substances.
(v) Air helps in the scattering of seeds and pollens of plants.
(vi) Air helps in the movements of sailing yachts, gliders, parachutes and airplanes.
Q.9. How do plants and animals help each other in the exchange of gases in the atmosphere?
Ans. Plants take carbon dioxide to give out oxygen. This oxygen is used by animals for respiration to expel out carbon dioxide. This carbon dioxide is used by plants to prepare food. This way, plants and animals help each other in the exchange of gases in the atmosphere