* Avogadro's Number: One mole of any substance contains 6.022 x 10^23 particles (atoms, molecules, etc.). This is known as Avogadro's number.

* Oxygen Molecule (O2): Each oxygen molecule (O2) consists of two oxygen atoms.

Calculation:

1. Atoms per molecule: 1 molecule of O2 has 2 oxygen atoms.

2. Atoms per mole: 1 mole of O2 has 6.022 x 10^23 molecules.

3. Total oxygen atoms: (2 atoms/molecule) * (6.022 x 10^23 molecules/mole) = 1.2044 x 10^24 oxygen atoms

Therefore, 1 mole of O2 gas has 1.2044 x 10^24 oxygen atoms.