Reducing Strength of Halide Ions

Steps:

• Concentrated H₂SO₄ reacts with NaBr to form HBr, which reduces H₂SO₄ to produce Br₂.
• With NaCl, H₂SO₄ forms HCl, but HCl does not reduce H₂SO₄ further.
• Br⁻ ions reduce sulfate to SO₂ and themselves oxidize to Br₂, per the reaction: 2Br⁻ + H₂SO₄ → Br₂ + SO₂ + H₂O.
• Cl⁻ lacks sufficient reducing power to oxidize by H₂SO₄, so only HCl forms.

Why D is correct:

• Br⁻ is a stronger reducing agent than Cl⁻ because bromide has lower electronegativity and easier loss of electrons, as per standard reduction potentials (E° Br₂/Br⁻ = +1.07 V vs. E° Cl₂/Cl⁻ = +1.36 V).

Why the others are wrong:

• A: Volatility affects distillation, not the redox reaction producing Br₂.
• B: HCl is a strong acid, not weak; acidity strength is irrelevant here.
• C: H₂SO₄ acts as a mild oxidizing agent toward Br⁻ but not Cl⁻.

Final answer: D