Which of the following can be classified as a mixture?

a no
pure air
pure gold
pure water
pure nitrogen

pure air

Explanation:

The different substances in a mixture are only physically combined but not chemically combined. When chemically combined, it becomes a compound. Pure air contains a mixture of gases such as nitrogen, carbon dioxide, and oxygen. The different gases can be physically separated (for example using densities) and without the use of chemical extraction (because they are not chemically bound to each other).

energy and particles