If a substance gains electrons, does it become oxidized or reduced?

When a substance gains electrons, it undergoes a reduction process. In biochemical terms, reduction refers specifically to the addition of electrons to a molecule, which decreases its oxidation state. This is part of a fundamental concept in redox (reduction-oxidation) reactions, where one substance is oxidized (loses electrons) and another is reduced (gains electrons).

In this context, gaining electrons leads to a more negative charge or a decrease in the oxidation state. For example, when oxygen is reduced, it gains electrons and may form a more stable compound, such as water when it reacts with hydrogen. Thus, the correct understanding is that the gain of electrons distinctly characterizes reduction, making the correct answer that a substance that gains electrons is reduced.