Oxidation of halides by concentrated sulfuric acid

Steps:

• Halogens follow reactivity order F > Cl > Br > I; stronger halogens displace weaker ones from compounds.
• Concentrated H₂SO₄ reacts with NaCl to form HCl gas without oxidation to Cl₂.
• With NaBr, H₂SO₄ first forms HBr, then oxidizes it to Br₂ due to Br⁻'s susceptibility.
• I₂ cannot displace Br⁻ from NaBr as I is less reactive than Br.

Why C is correct:

• Concentrated H₂SO₄ oxidizes Br⁻ to Br₂ via 2HBr + H₂SO₄ → Br₂ + SO₂ + 2H₂O, producing bromine from sodium bromide.

Why the others are wrong:

• A: Br₂ cannot displace Cl⁻ from NaCl as Cl is more reactive than Br.
• B: NaCl + conc. H₂SO₄ → NaHSO₄ + HCl; no Cl₂ produced as Cl⁻ resists oxidation.
• D: I₂ in aqueous KI cannot displace Br⁻ from NaBr as I is less reactive than Br.

Final answer: C