A molecule of oxygen gas (O₂) is made up of two oxygen atoms bonded together.

Here's a breakdown:

* Oxygen atom: Oxygen is an element found on the periodic table. Each oxygen atom has 8 protons in its nucleus.

* Bonding: The two oxygen atoms in O₂ are held together by a double covalent bond. This means they share two pairs of electrons, creating a strong and stable bond.

So, the answer is two oxygen atoms.