What does reduction involve in terms of electron transfer?

Reduction is defined as a process that involves the gain of electrons by an atom, ion, or molecule. When an entity undergoes reduction, its oxidation state decreases because it acquires additional negatively charged particles (electrons). This is a crucial concept in redox (reduction-oxidation) reactions, where one species is reduced while another is oxidized.

In a typical redox reaction, the species gaining electrons is the one being reduced, whereas the species losing electrons is the one being oxidized. This understanding is fundamental when analyzing reactions, predicting outcomes, and balancing chemical equations. Therefore, the correct answer reflects the core principle of reduction in terms of electron transfer. In contrast, the other options pertain to processes that do not accurately describe reduction—loss of electrons corresponds to oxidation, and changes involving protons do not directly relate to the definition of redox reactions.