Question

What is the relationship between diatomic molecules and diatomic elements?

Answer 1

Diatomic elements are a subgroup of diatomic molecules.

Explanation:

Every molecule that consists of two atoms is diatomic. Only if the two atoms are the same there is a diatomic element.

So `O_2` is a diatomic element (and thus a diatomic molecule)
`HCl` is a diatomic molecule, but not a diatomic element.