A redox reaction is a chemical reaction in which the oxidation number of a participating chemical species varies. In this type of chemical reaction, oxidation and reduction take place simultaneously. Oxidation is the loss of electrons, while reduction is the gain of electrons. A few examples of redox reactions are:

• The reaction between Zinc and Copper: Zn (s) + CuSO4 (aq) → ZnSO4 (aq) + Cu (s). Here, Zinc gets oxidized and acts as a reducing agent, while CuSO4 gets reduced and acts as an oxidizing agent.

• The reaction between lead oxide (PbO) and ammonia (NH3): 3 PbO (s) + 2 NH3 (g) → N2 (g) + 3 H2O (l) + 3 Pb (s). In this reaction, the oxidation number of lead decreases from +2 to 0, and Pb is reduced. The oxidation number of nitrogen increases from -3 to zero, meaning N is oxidized.

• The reaction between Magnesium and Oxygen: Mg (s) + O2 (g) → MgO (s). In this reaction, Mg loses two electrons and becomes an Mg2+ cation. Its oxidation number goes from zero to +2, hence it is oxidized. The oxidation part of the reaction is written as: Mg (s) → Mg2+ + 2 e–. Oxygen gains two electrons and becomes an oxide ion (O2–). Its oxidation number goes from zero to -2, hence it is reduced. The reduction part of the reaction is written as: O2 (g) + 4 e– → 2 O2– (g) .

Redox reactions have numerous industrial and everyday applications, such as in batteries, electroplating, and corrosion prevention.