Here's why:

* Molecule: A molecule is formed when two or more atoms bond together.

* Element: An element is a pure substance consisting of only one type of atom.

* Oxygen: Oxygen is a chemical element with the symbol O.

In the case of oxygen gas (O2), two oxygen atoms bond together to form a molecule. This is why we breathe oxygen, as the diatomic (two-atom) molecule is the stable form of oxygen in the air.