Air present everywhere around us. Air has no colour and one can see through it. It is transparent.
The earth is surrounded by a thin layer of air. This layer extends up to many kilometers above the surface of the earth and is called atmosphere.
Air is a mixture of many gases.
Water vapour
We have learnt earlier that air contains water vapour. When air comes in contact with a cool surface, it condenses and drops of water appear on the cooled surfaces.
Oxygen
Oxygen is the essential substance for our life, we use it in the breathing and in various way. It's the component of air, which supports burning, is known as oxygen.
Nitrogen
The presence of some component in the air, which does not support burning. The major part of air (which does not support burning candle) is nitrogen.
Carbon dioxide
Carbon dioxide makes up a small component of the air around us. Plants and animals consume oxygen for respiration and produce carbon dioxide. Plant and animal matter also consumes oxygen on burning and produces mainly carbon dioxide and a few other gases. It is advisable not to burn dry leaves and discarded remains of the crop, which pollute our surroundings.
Dust and smoke
The burning of fuel also produces smoke. Smoke contains a few gases and fine dust particles and is often harmful.
Dust particles are always present in air. The presence of dust particles in air varies from time to time, and from place to place.
These bubbles come from the air dissolved in water. As we learnt that the Oxygen is exits in the air. When you heat the water, to begin with, the air dissolved in it escapes. As you continue heating, the water itself turns into vapour and finally begins to boil.
When the water is poured on the lump of soil, it displaces the air which is seen in the form of bubbles.
While plants make their own food and oxygen is produced along with it. Plants also consume oxygen for respiration, but they produce more of it than they consume.
The balance of oxygen and carbon dioxide in the atmosphere is maintained through respiration in plants and animals and by the photosynthesis in plants.