No, air is not a pure substance. Air is a mixture of several gases, primarily nitrogen (about 78%) and oxygen (about 21%), with small amounts of other gases like argon, carbon dioxide, and trace amounts of other elements and compounds.
A pure substance is a material that has a constant composition and consistent properties throughout the sample. Examples of pure substances include elements like gold or compounds like water. Since air is a mixture of different gases, it does not have a fixed composition and its properties can vary depending on the proportions of the gases present.
In summary, air is considered a mixture rather than a pure substance because it is composed of multiple gases that are not chemically bonded to each other.