NCERT 6th Class (CBSE) Science: Air Around Us

Question: Describe balance of oxygen in the air.

Answer: The oxygen in air is used by the organisms present in air, water or soil or on earth for their respiration. During respiration carbon dioxide gas is released to air. But green plants during photosynthesis use carbon dioxide of air for preparing food and they release oxygen gas in the air. Thus the balance of oxygen in air is maintained.

Question: What happens if the percentage of oxygen in the air reaches to 70%?

Answer: If any substance catches fire it will become difficult to extinguish the fire, as oxygen supports combustion.

Question: What happens if the percentage of carbon-dioxide increases in the air?

Answer: The increased percentage of carbon-dioxide will cause green house effect, i.e. it will not allow the hot rays of sun to escape from the atmosphere after reflection once they enter the earth’s atmosphere, thereby increasing the temperature of earth, ice on mountains will melt and water level will rise.

Question: You must have seen during rainy season, when it rains the animals like earthworm, snakes, snails etc. are commonly seen. Explain why?

Answer: All these animals live in underground burrows or remain buried in the soil. They get oxygen from air that enters into the burrow through entrance of burrow or through pores in the soil. But when it rains, the water gets filled in their dwelling places and pores of the soil. So, they come out in search of air.

Question: Why is carbon-dioxide gas used to extinguish fire?

Answer: It is because carbon-dioxide does not support combustion. When sprayed on burning object it stops the supply of oxygen and extinguishes fire.

Question: How will you prove that soil contains air in it?

Answer: Take a glass tumbler add some soil in it, then pour some water on the soil slowly, the air-bubbles comes out of the soil. This proves that soil holds air in it.

Question: Why do we see the sky and air clear and clean after rainfall?

Answer: The dust particles which remain suspended in air get loaded and come down on the ground due to rainfall, this is the reason that the sky and the air look clean and clear after rainfall.

Question: Explain why mountaineers carry oxygen cylinders with them?

Answer: As you go up, above the sea-level the atmospheric pressure goes on decreasing and the amount of oxygen also decreases at higher altitude.