Sulfuric acid oxidizes bromide and iodide but not chloride

Steps:

• Concentrated H₂SO₄ reacts with NaCl to form HCl gas without oxidation, as Cl⁻ is not easily oxidized.
• With NaBr, H₂SO₄ oxidizes Br⁻ to Br₂ (via SO₄²⁻ + 2Br⁻ → SO₄²⁻ + Br₂ + 2e⁻), producing reddish-brown fumes.
• With NaI, H₂SO₄ oxidizes I⁻ to I₂ (via SO₄²⁻ + 2I⁻ → SO₄²⁻ + I₂ + 2e⁻), forming violet vapors.
• Oxidation occurs only for Br⁻ and I⁻ due to their lower reduction potentials compared to Cl⁻.

Why C is correct:

• H₂SO₄ acts as an oxidizing agent with NaBr and NaI because the standard reduction potential of SO₄²⁻/SO₂ (0.17 V) is sufficient to oxidize Br⁻ (-1.07 V) and I⁻ (-0.54 V), but not Cl⁻ (-1.36 V).

Why the others are wrong:

• A: H₂SO₄ does not oxidize Cl⁻, only displaces it as HCl.
• B: Includes NaCl, which undergoes no oxidation.
• D: Excludes NaBr, which is oxidized to Br₂.

Final answer: C