Question

what happens when a substance is oxidized?
it loses electrons.
it releases oxygen.
it gains electrons.
it becomes an oxygen atom.

Explanation:

In redox (reduction - oxidation) reactions, oxidation is defined as the loss of electrons. A substance that is oxidized loses electrons. Releasing oxygen is not the definition of oxidation (for example, in reactions like the oxidation of iron in the presence of oxygen and water, iron loses electrons). Gaining electrons is reduction, not oxidation. And a substance being oxidized does not mean it becomes an oxygen atom.

Answer:

It loses electrons.