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

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

Answer: (B)

Verified step by step guidance

1. Recall that a reduction process involves the gain of electrons by a species, which means the species' oxidation state decreases.
2. Examine each half-reaction to determine whether electrons are on the reactant side (indicating reduction) or on the product side (indicating oxidation).
3. For the half-reaction \(Fe^{2+} \rightarrow Fe^{3+} + e^-\), electrons are produced on the product side, so this is an oxidation, not a reduction.
4. For the half-reaction \(Cu^{2+} + 2e^- \rightarrow Cu\), electrons are on the reactant side, indicating that \(Cu^{2+}\) gains electrons to form \(Cu\), which is a reduction.
5. Similarly, check the other half-reactions: \(Cl_2 \rightarrow 2Cl^- + 2e^-\) produces electrons (oxidation), and \(Zn \rightarrow Zn^{2+} + 2e^-\) also produces electrons (oxidation). Therefore, the correct reduction half-reaction is \(Cu^{2+} + 2e^- \rightarrow Cu\).