An oxidation–reduction (redox) reaction is a reaction in which oxidation numbers change and electrons are transferred from one reactant to another. Oxidation (loss of electrons) and reduction (gain of electrons) always occur together, since electrons released by one species must be taken up by another. Redox reactions underlie combustion, corrosion, respiration, and the working of batteries.

氧化还原反应是氧化数发生变化、电子从一种反应物转移到另一种反应物的反应。氧化(失去电子)和还原(得到电子)总是同时发生,因为一种物质放出的电子必须被另一种物质接受。氧化还原反应是燃烧、腐蚀、呼吸作用以及电池工作的基础。