Air is a mixture but not compound. Its constituents can be separated. For example: oxygen, nitrogen etc.

Is air a compound?

Nearly all of the Earth's atmosphere is made up of only five gases: nitrogen, oxygen, water vapor, argon, and carbon dioxide. Several other compounds are also present. Although this CRC table does not list water vapor, air can contain as much as 5% water vapor, more commonly ranging from 1-3%.

Why air is a mixture or compound?

Air is a mixture and not a compound because: Air does not have a formula like a mixture, while compounds have a fixed formula. When air is formed by gases, there is no energy change. Properties of air are variable and subjective to time and place.