Question

consider the redox reaction below.
mg(s) + fe²⁺(aq) → mg²⁺(aq) + fe(s)
which equation is a half reaction that describes the reduction that is taking place?
○ fe²⁺(aq) + 2e⁻ → fe(s)
○ mg(s) → mg²⁺(aq) + 2e⁻
○ fe²⁺(aq) → fe(s) + 2e⁻
○ mg(s) + 2e⁻ → mg²⁺(aq)

Explanation:

1. Reduction Definition: Reduction is the gain of electrons (or decrease in oxidation state).
2. Analyze $\ce{Fe}$ Species: In the reaction, $\ce{Fe^{2+}}$ (oxidation state +2) becomes $\ce{Fe(s)}$ (oxidation state 0), so it gains electrons.
3. Evaluate Options:

• Option A: $\ce{Fe^{2+}}$ gains $2e^-$ to form $\ce{Fe(s)}$ (reduction, correct).
• Option B: $\ce{Mg}$ loses electrons (oxidation, not reduction).
• Option C: $\ce{Fe^{2+}}$ losing electrons (oxidation, incorrect for reduction).
• Option D: $\ce{Mg}$ gaining electrons while forming $\ce{Mg^{2+}}$ (contradicts oxidation state change, incorrect).

Answer:

A. $\ce{Fe^{2+}_{(aq)} + 2e^- \longrightarrow Fe_{(s)}}$