What is reduction?

The most commonly understood definition of reduction is the removal of oxygen or addition of hydrogen ions. However, chemically, reduction can be defined as gain of electrons just as oxidation is loss of electrons. Let us look at the illustration:

Thus, the substance that a gains electron is reduced and that loses electrons is oxidized. In the above equations, cupric gains electrons and becomes cuprous in reduction and vice versa in oxidation. In an oxidation-reduction reaction, the electron donor is oxidized and the electron acceptor is reduced. See the reaction below:

2Na + Cl₂ → NaCl

The sodium is oxidized since it has lost electrons and chloride is reduced as it has gained those electrons. In organic reactions, oxidation-reduction reactions usually involve loss or gain of hydrogen. Thus, to summarize, reduction is gain of electrons, gain of hydrogen or removal of oxygen and oxidation is loss of electrons, gain of oxygen or loss of hydrogen.