Question

which equation describes a reduction?
○ mg(s) ⟶ mg²⁺(aq) + 2e⁻
○ 2cl + 2e⁻ ⟶ 2cl⁻
○ na(s) ⟶ na⁺(aq) + e⁻
○ al(s) ⟶ al³⁺(aq) + 3e⁻

Explanation:

Step1: Recall reduction definition

Reduction is gain of electrons (or decrease in oxidation state).

Step2: Analyze each option

• Option 1: \( \text{Mg}(s) \longrightarrow \text{Mg}^{2+}(aq) + 2\text{e}^- \)

Mg loses electrons (oxidation), so not reduction.

• Option 2: \( 2\text{Cl} + 2\text{e}^- \longrightarrow 2\text{Cl}^- \)

Cl gains electrons (oxidation state decreases from 0 to -1), so this is reduction.

• Option 3: \( \text{Na}(s) \longrightarrow \text{Na}^+(aq) + \text{e}^- \)

Na loses electrons (oxidation), not reduction.

• Option 4: \( \text{Al}(s) \longrightarrow \text{Al}^{3+}(aq) + 3\text{e}^- \)

Al loses electrons (oxidation), not reduction.

Answer:

B. \( 2\text{Cl} + 2\text{e}^- \longrightarrow 2\text{Cl}^- \)