Oxidation–reduction reactions, commonly known as redox reactions. A redox reaction is defined as a reaction in which oxidation and reduction take place simultaneously. These type of reactions that involve the transfer of electrons from one species to another. The species that loses electrons is said to be oxidized, while the species that gains electrons is said to be reduced.
(i) Cu²⁺ + 2e⁻ ⟶ Cu(s) (reduction half reaction)
(ii) Zn(s) ⟶ Zn²⁺ + 2e⁻ (oxidation half reaction)