Which statement describes a reduction half-reaction?

Which statement describes a reduction half-reaction?

• A. Electrons are being added to the reactants.
• B. Electrons are being removed from the reactants.
• C. The oxidation state increases for the reduced species.
• D. Protons are consumed in the reaction.

Answer: (A)

Reduction is defined by the gain of electrons by a species. In a reduction half-reaction, electrons are added to the reactant to produce the reduced product, so the electrons appear on the reactant side of the half-reaction. That is why the statement describing electrons being added to the reactants best captures the essence of a reduction half-reaction, and why the oxidation counterpart would involve electrons on the product side. Also, the reduced species actually decreases in oxidation state, not increases, and while protons may be involved in some redox contexts, their presence is not what defines reduction.

Reduction is defined by the gain of electrons by a species. In a reduction half-reaction, electrons are added to the reactant to produce the reduced product, so the electrons appear on the reactant side of the half-reaction. That is why the statement describing electrons being added to the reactants best captures the essence of a reduction half-reaction, and why the oxidation counterpart would involve electrons on the product side. Also, the reduced species actually decreases in oxidation state, not increases, and while protons may be involved in some redox contexts, their presence is not what defines reduction.