AIR The air we breathe is necessary to keep us alive but it is also a chemical resource Air is a mixture of gases and which can be seperated by fractional distillation of liquid air COMPOSITION OF AIR Composition of air is appriximately constant throughout the world But it can change with the increased rate of air pollution Nitrogen 79 Oxygen 20 Carbon dioxide Water vapour Remaining includes the noble gases mainly argon Air also include pollutants such as sulphur dioxide oxide of nittogen etc and their composition varies from place to place