Why does air not have a definite formula?

This is what i found “nuclear fuel is material used in nuclear power stations to produce heat to power turbines. heat is created when nuclear fuel undergoes nuclear fission. most nuclear fuels contain heavy fissile actinide elements that are capable of undergoing and sustaining nuclear fission.” i hope this you for what your looking for. can you plz mark me brainliest?

The density would be 1.622