An oxidizing agent (also called an oxidant, oxidizer or oxidiser) can be defined as either: a chemical compound that readily transfers oxygen atoms, or a substance that gains electrons in a redox chemical reaction In both cases, the oxidizing agent becomes reduced in the process. In simple terms: The oxidizing agent's reduced. The reducing agent's oxidized. All atoms in a molecule can be assigned an oxidation number. This number changes when an oxidant acts on a substrate. Redox reactions… (More on Oxidant)