Reduction can be defined as what process?

Reduction is defined as the gain of electrons by a substance during a chemical reaction. This process typically results in a decrease in the oxidation state of the element that is being reduced. When a species gains electrons, it often becomes more negatively charged or less positive, which aligns with the fundamental definition of reduction in redox (reduction-oxidation) reactions.

In the context of redox reactions, reduction can occur simultaneously with oxidation, where one species loses electrons (oxidation). By understanding this process, you can recognize that reduction is integral to many biochemical pathways and energy transfer systems, as it often accompanies energy capture or storage mechanisms.

The other options describe processes that do not accurately define reduction in terms of electron transfer. For example, loss of hydrogen and gain of oxygen typically involve oxidation rather than reduction, and loss of protons does not capture the essence of reducing agents or the electron gain characteristic of reduction. Therefore, associating reduction specifically with the gain of electrons is key to comprehending redox reactions and their implications in chemistry and biology.