Question

Why does oxygen exist?

Answer 1

Because there are O2 molecules in nature

hope this helps you

Answer 2

Atoms always try to have full “shells” of electrons. If they have not enough electrons to make full shells, they can find more by sharing electrons with another atom. For the halogen gases, and oxygen, nitrogen and hydrogen, this is easily accomplished by pairing up.

Elemental oxygen is not only found in pairs: it can also be found in the form of ozone, a molecule with 3 oxygen atoms.