* If "O" refers to the element oxygen: Then there is 1 atom in "O". "O" is the chemical symbol for oxygen, and it represents a single atom of oxygen.
* If "O" refers to a molecule of oxygen gas: Then there are 2 atoms in "O". Oxygen gas exists as a diatomic molecule, meaning it has two oxygen atoms bonded together (O₂).
So, the answer depends on the context. Please clarify what "O" represents for a definitive answer.
