What is the composition of air?

Phases of Matter and Intensive Properties Read more from
Chapter MacRoscopic Properties: The World We See

Earth’s atmosphere is made up of 78% nitrogen (N2) and 21% oxygen (O2), if you ignore water vapor, which shifts too much to include in averages for the entire planet. The last 1% is made up of mostly argon (Ar), followed by carbon dioxide (CO2) and other trace gases.