Is air a pure substance or a mixture?

Air is a mixture, which is primarily made up of nitrogen and oxygen. It is more nitrogen than oxygen, with about 78 percent of the makeup being the nitrogen and 21 percent oxygen.

The other elements that make up air are generally microscopic or undetectable to people. Water is one of the most abundant components of the mixture, but it still makes up less than 1 percent of the overall mixture of air. Dust, ozone, pollen and spores are also found in air, but most of these particles are so small that they can not be seen without a microscope.