An oxide ion (O^2-) is oxidized to an oxygen atom (O) by gaining electrons.

Here's why:

* Oxidation is the process of losing electrons.

* Reduction is the process of gaining electrons.

In this case, the oxide ion (O^2-) has gained two electrons compared to a neutral oxygen atom (O). To return to its neutral state, it needs to *lose* those two electrons, which is an oxidation process.

Example:

The reaction of an oxide ion with a strong oxidizing agent like fluorine can lead to this oxidation:

2O^2- + F₂ → 2O + 2F^-

Here, the oxide ions (O^2-) lose electrons and are oxidized to oxygen atoms (O), while the fluorine molecules (F₂) gain electrons and are reduced to fluoride ions (F^-).