Which term best fits the definition: in chemistry, the gain of electrons?

• A. Oxidation
• B. Reduction
• C. Hydration
• D. Dehydration

Answer: (B)

Reduction is the gain of electrons. In redox reactions, electrons move from one species to another, and the one that gains electrons is reduced, with its oxidation state decreasing. For example, chlorine gas can gain two electrons to become chloride ion, a reduced form. Oxidation, by contrast, is the loss of electrons and an increase in oxidation state. Hydration and dehydration involve adding or removing water, not electron transfer, so they don’t describe electron gain or loss. A simple rule to remember: reduction equals gain of electrons (lower oxidation state); oxidation equals loss of electrons (higher oxidation state).