Which of the following is not an element?

Air is not an element.
Air is the mixture of different gases in the atmosphere. The percent of gases present in the air are nitrogen(78%), argon(0.93%), and oxygen 20%. This percentage is changed with a change in altitude. In the mixture of air, individual gases retain their properties and they can be easily separated. At a higher level, air contains ozone, helium, and hydrogen. We notice the presence of air when the wind blows.