Redox Strength of Halide Ions

Steps:

• Concentrated H₂SO₄ reacts with NaCl to displace HCl, forming NaHSO₄, as Cl⁻ is not oxidized.
• With NaBr, Br⁻ is oxidized to Br₂ gas, while H₂SO₄ is reduced to SO₂ or H₂S.
• This oxidation occurs because Br⁻ donates electrons more readily than Cl⁻.
• The standard reduction potential for Br₂/Br⁻ (+1.07 V) is lower than Cl₂/Cl⁻ (+1.36 V), making Br⁻ a stronger reducing agent.

Why D is correct:

• Br⁻ reduces H₂SO₄ (E° ≈ +0.17 V for SO₄²⁻/SO₂) to produce Br₂, per the half-reaction 2Br⁻ → Br₂ + 2e⁻, which is favorable unlike for Cl⁻.

Why the others are wrong:

• A: Volatility affects boiling points but not the redox reaction producing Br₂.
• B: HCl is a strong acid; its strength is irrelevant to oxidation.
• C: Concentrated H₂SO₄ oxidizes Br⁻ but not Cl⁻ due to potential differences.

Final answer: D