What is air, you may ask? Well, air is a mixture, which is what we’ve been discussing. Air makes up the atmosphere around us, and is composed almost entirely of nitrogen and oxygen. Nitrogen is 78% of the atmosphere by volume, and if you remember your ideal gas laws, that means it is also 78% by mole composition and 78% by partial pressure. (This means 78% of the molecules in air are nitrogen, and if atmospheric pressure is 1 atm then 0.78 atm is the pressure of nitrogen.)
The ~1% of air that isn’t nitrogen or oxygen has many other things in it, argon and carbon dioxide being the main two. In the graphic above (which the Clear Science staff has borrowed from the Wikipedia page on air), you can see that the trace gases in air like hydrogen and krypton are very dilute.
Air is a solution, which is a type of mixture that is homogeneous. Separating air into components requires a trick, such as cryogenic cooling. (BTW, air also has water in it, but the amount varies widely. That is measure by humidity.)