What is the air we breathe made up of? What is the most common element in it? Why is air consider a mixture?

The majority of the air we breathe is made up of nitrogen and oxygen, though you'll also find argon, carbon dioxide and other gases in trace amounts.

It is made up of about 78% nitrogen, 21% oxygen, and many other elements like argon, water vapor, and other things. The most common element of air is nitrogen, and it is considered a mixture because we can distinguish between the elements in the air we breath, and we can physically separate the elements in the air.