How is reduction related to the gain of electrons?

In chemistry, reduction is defined as a process in which the number of electrons associated with an atom or a group of atoms increases. This gain of electrons is a fundamental criterion for identifying a reduction reaction.12

When a chemical species undergoes reduction, it effectively takes up electrons supplied by another substance, which is simultaneously oxidized. This transfer of electrons from a reducing agent to an oxidizing agent is the core mechanism of oxidation-reduction (redox) reactions.13

The relationship between reduction and electron gain can be summarized as follows:

• Charge Reduction: The gain of electrons results in a decrease in the real or apparent electric charge of the atom being reduced.3
• Oxidation State: In terms of oxidation numbers, a decrease in an atom's oxidation number corresponds to reduction.2
• Electrochemical Context: In electrochemical processes, a species is reduced when it takes an electron from an electrode. Conversely, the electromotive series ranks chemical species based on their inherent tendency to gain electrons (be reduced) or lose them (be oxidized).45