Air is a mixture of various gases, water vapor, dust and microbes. All the constituents of air are mixed in any proportion and are not chemically bonded. These gases and water vapor are not uniformly distributed everywhere and this is why air is considered a mixture.
Air contains 78.084 percent nitrogen gas, 20.946 percent oxygen, 0.04 percent carbon dioxide and other gases, such as carbon monoxide and argon, in minute quantities. Air envelops the Earth’s surface and extends to a height of 62 miles. At this height, air becomes too rarefied to support life in any form. The air forms a protective layer and prevents the Earth from getting too hot.