Oxygen (O2) is an example of a gas that exists as a molecule.

Here's why:

* Diatomic: Oxygen gas is composed of two oxygen atoms bonded together, forming a diatomic molecule.

* Gaseous state: At standard temperature and pressure (STP), oxygen exists as a colorless, odorless gas.

Other examples of gases that exist as molecules include:

* Nitrogen (N2)

* Hydrogen (H2)

* Carbon dioxide (CO2)

* Methane (CH4)

* Chlorine (Cl2)

* Ozone (O3)