Which of the following half-reactions represents a reduction process?

• A. Fe^{2+} ightarrow Fe^{3+} + e^-
• B. Zn ightarrow Zn^{2+} + 2e^-
• C. Cl_2 ightarrow 2Cl^-
• D. Cu^{2+} + 2e^- ightarrow Cu

Answer: (D)

Verified step by step guidance

1. Understand that a reduction process involves the gain of electrons by a species. In half-reactions, electrons appear on the reactant side for reduction.
2. Examine each half-reaction to identify where electrons are on the reactant side, indicating reduction:
3. - For \(Fe^{2+} \rightarrow Fe^{3+} + e^-\), electrons are produced on the product side, indicating oxidation.
4. - For \(Zn \rightarrow Zn^{2+} + 2e^-\), electrons are also on the product side, indicating oxidation.
5. - For \(Cl_2 \rightarrow 2Cl^-\), electrons are not explicitly shown, but since chlorine is going from elemental form to ions, it gains electrons (reduction). The correct reduction half-reaction explicitly shows electrons on the reactant side, such as \(Cu^{2+} + 2e^- \rightarrow Cu\).