Composition of air
Various activities have shown that the composition of air on the earth by volume is as given in the table.
Gases in air
Percentage by volume
Other inert gases
We may have noticed that when shiny iron rods are exposed in a moist place for few days, their outer surface becomes reddish brown. The reddish brown layer on the surface of the iron rod is called rust. This brown rust is reddish due to the oxides of the iron. Thus, the process of formation of rust by the slow oxidation of iron into oxide due to the atmospheric oxygen in the presence of water vapour is called rusting.
Presence of oxygen in air
Carbon dioxide in air
Carbon dioxide in the air is used by plants to make their food during the process of photosynthesis. It is given off during the process of respiration by all living things. It is also produced when fuels are burnt in air.