How will you justify that air is a mixture and not a compound?
air is a mixture because it is made up of different gases
Air is a mixture; the properties of the constituents of air (oxygen, nitrogen, carbon dioxide etc.) are not changed, and the mass ratios among them are not as consistent as they would be if air were a compound. On distillation of liquefied air, nitrogen predominantly distills off first, leaving behind oxygen in the liquid form. This is characteristic of a mixture, not of a compound.
Liquid air is a mixture not a compound. As we know that air is a mixture of different gases. It contains 78% nitrogen and 21% oxygen and remaining 1% is comprising various other gases. The process of preparing liquid air does not involve any chemical reaction and hence no compound is formed. It is basically a physical process involving compression of air as well as cooling simultaneously. Thus liquid air remains a mixture.