What does reduction refer to in a chemical reaction?

Reduction in a chemical reaction refers to the process in which a molecule gains an electron. This gain in electrons decreases the oxidation state of the molecule, which contrasts with oxidation where a molecule loses electrons and increases its oxidation state. The concept of reduction is essential in understanding redox (reduction-oxidation) reactions, which are fundamental to many biochemical processes, such as cellular respiration.

In addition to gaining electrons, reduction often involves the addition of hydrogen or the removal of oxygen from a molecule, reinforcing its role in energy transfer and metabolism. Understanding that reduction involves the gain of electrons helps clarify the essential relationship between reduction and oxidation, where these processes always occur simultaneously in a reaction.