The composition of air is- 78Nitrogen 21Oxygen and 1 Other. Why air is a mixture not a compound give any three reasons. Selina Concise Chemistry Class 6 Icse Solutions Chapter 5 Pure Substances And Mixtures Separation Of Mixture Chemistry Class Chemistry Middle School Chemistry By physical process of fractional distillation. . The composition of air is- 78Nitrogen 21Oxygen and 1 Other inert gases like Hydrogen Argon. Air is a mixture not a compound for following reasons. Air is considered a mixture because of the following reasons. 2 there is variable composition. I Air can be separated into its constituents like oxygen nitrogen etc. Air does not have a formula like a mixture while compounds. In case of air the majority of it contains nitrogen and oxygen. Q1 Explain why air is considered a mixture and not a compoundismatterarounduspure extraquestions. Internal combustion engines are 4 stroke.