Test: Air Around Us - Class 6 MCQ

Oxygen is necessary for combustion, respiration and oxidation.

Air is not required for boiling water but required for inflating tyres, filling balloon and winnowing.

During rain, soil animals come out from their burrows for respiration as their burrow is filled by water.

The balance between carbon dioxide and oxygen is maintained by photosynthesis and respiration in which carbon dioxide and oxygen is used and oxygen and carbon dioxide is produced respectively.

The density of air decreases with an increase in altitude.

Plants play an important role in the oxygen cycle, as they release oxygen during the process of photosynthesis. Thus, they help in balancing the oxygen content in the atmosphere.

The density of air decreases with altitude, so the oxygen needed for breathing also decreases and becomes difficult to breathe. Hence, mountaineers carry oxygen cylinders.

Carbon dioxide traps the reflected rays of the sun that fall on the earth's surface. This results in the increase of the earth's temperature, which is referred as global warming.

High levels of carbon dioxide in the atmosphere cause the harmful greenhouse effect.

If we breathe air through our mouth, the dust particles present in the air may enter the lungs and cause harm. But if the nose is used for breathing, the hair present in the nose filters the air and prevents the dust particles from entering the lungs.