Science [3 Marks Each] QUE-ANS

Air is dissolved in water in the form of oxygen. When water bottle is left in the open sunlight, tiny bubbles were formed all around inside the bottle because air dissolved in water starts escaping in the form of tiny bubbles due to heat from the sun.

Plants utilize carbon dioxide present in the atmosphere for the process of photosynthesis. They release oxygen in the atmosphere. This oxygen is inhaled by humans and in turn, carbon dioxide is exhaled.

In this way, plants and animals help each other in exchange of gases in the atmosphere.

The level of oxygen is maintained in the atmosphere by planting more and more trees and by avoiding excessive burning of fuels. The plants will take up the carbon dioxide in the atmosphere to make their food and in turn will release oxygen. This oxygen is taken up by animals, including humans, for respiration and in turn release carbon dioxide.

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.

The leaves and flowers of the roadside plants are very dull because the air along the roadside is polluted with air pollutants due to emissions from vehicles and industries, etc.
Thus, the roadside plants had probably some dust and soot deposited on them. This made them to appear dull.

1. Oxygen: There will be no life on the earth. Oxygen is vital for life. It helps in burning, respiration, photosynthesis, etc. Oxygen is basic need of all living beings.
2. Nitrogen: Nitrogen does not support burning. If nitrogen gas disappear from the atmosphere, things will burn very fast.
3. Carbon dioxide: Carbon dioxide is needed for photosynthesis which occurs in green plants. In its absence, plants will not be able to prepare their food and hence, without carbon dioxide there would be no plants or animals on the earth.

1. Oxygen.
2. Carbon dioxide.
3. Carbon dioxide.
4. Nitrogen.
5. Oxygen.

1. Air is dissolved in water in the form of oxygen. Tiny bubbles are formed, when air present in the water escape on boiling it.

So, tiny bubbles appeared due to the evolution of air dissolved in water.

2. No, tiny bubbles will not appear as there is no dissolved air in this water.

1. Mask is covering the nose and mouth of the policeman.
2. Policeman is putting a cover on his nose to save himself from dirt/polluted air.
3. Air quality of the place is not good. It is due to the smoke and gases emitted by the automobiles along with dust particles present in the air.

• Take three candles, two glass jars that can cover two candles but of different sizes and a watch.
• Light all the three candles at one time after fixing them on the table. Cover two candles with the jars. Leave one candle uncovered. Switch off the fan and close doors and windows. This will stop wind from blowing off the candles.
• After some time the candle covered with the small jar goes off first. Then the one with a bigger jar goes off. The candle in the open continues to burn. Thus, air supports burning.

1. The wind makes the windmill rotate.
2. Air is a mixture of some gases.
3. A weather cock shows the direction in which the air is moving at that place.
4. Mountaineers carry oxygen cylinders with them, while climbing high mountains.

1. When the glass is tilted, the air present in the glass is rapidly replaced with water.

2. For burning, oxygen is required. When covered, the candle does not get access to oxygen, hence it extinguishes.

3. When the candle extinguishes, the temperature inside the jar decreases and the temperature drops. To equalise the pressure, water enters into the jar.