Which of the following is an example of reduction?

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

Answer: (D)

Verified step by step guidance

1. Understand the concept of reduction: Reduction is the gain of electrons by a species. In a redox reaction, the species that gains electrons is reduced.
2. Analyze each given reaction to identify if electrons are gained or lost. For example, in the reaction \(\text{Zn} \rightarrow \text{Zn}^{2+} + 2e^-\), zinc loses electrons, so this is oxidation, not reduction.
3. Look at the reaction \(\text{Cl}_2 \rightarrow 2\text{Cl}^-\): chlorine molecules gain electrons to form chloride ions. Since electrons are gained, this is a reduction reaction.
4. Examine \(\text{Cu}^{2+} \rightarrow \text{Cu} + 2e^-\): copper ions lose electrons to form copper metal, which means this is oxidation, not reduction.
5. Consider \(\text{Fe}^{3+} + e^- \rightarrow \text{Fe}^{2+}\): iron(III) ions gain an electron to become iron(II) ions, indicating a gain of electrons and thus a reduction process.