By Anne Marie Helmenstine, Ph.D. Definition: An oxidant is a reactant that removes electrons from other reactants during a redox reaction. Also Known As: oxidizer, oxidizing agent. Examples: Hydrogen peroxide, ozone, and nitric acid are all oxidizers.y Anne Marie Helmenstine, Ph.D. Definition: An oxidant is a reactant that removes electrons from other reactants during a redox reaction. Also Known As: oxidizer, oxidizing agent. Examples: Hydrogen peroxide, ozone, and nitric acid are all oxidizers.