An oxidiser, also known as an oxidant or oxidising agent, is a reactant, a substance that takes part in and undergoes change during a reaction that draws electrons away from other reactants during a redox reaction. Any chemical reaction in which the oxidation numbers (oxidation states) of the atoms are changed is an oxidation-reduction reaction. Such reactions are also known as redox reactions, which is shorthand for reduction-oxidation reactions.1
Common oxidizing agents include: hydrogen peroxide, ozone, oxygen, potassium nitrate, and nitric acid are all oxidizing agents. All of the halogens are oxidizing agents (e.g., chlorine, bromine, fluorine).