Reduction Definition

Definition: A half-reaction in which a chemical species decreases its oxidation number, usually by gaining electrons.

Examples: The H⁺ ions, with an oxidation number of +1, are reduced to H₂, with an oxidation number of 0, in the reaction: Zn(s) + 2H⁺(aq) → Zn²⁺(aq) + H₂(g).