The composition of air is not the same in all places. The percentage of oxygen decreases in the air at higher altitudes. Similarly, the air in industrial areas has more carbon dioxide gas and other polluting gases than the air in the countryside.
The main constituents of air can be separated by physical methods, such as liquefaction and fractional distillation.
No chemical action takes place when the constituents of air, i.e., oxygen, nitrogen, water vapor, and carbon dioxide are mixed. Thus, when its constituents are mixed, no heat or light energy is evolved or absorbed.
Each of the constituents of air retains its physical and chemical properties. For example, oxygen helps in combustion, carbon dioxide lowly turns limewater milky, etc.
