Answer
When oxidation and reduction takes place simultaneously it is called a redox reaction.
Explanation:
Oxidation is the process in which an electron loses an atom, whereas, in reduction an atom gains an atom. when both of these reactions occur simultaneously the process is known as redox.
When a substance is being oxidized, it loses an electron or a hydrogen atom and gains an oxygen atom. Whereas, in reduction it gains an hydrogen atom and loses an oxygen atom. These two cannot happen individually and will always happen simultaneously.
