Redox reaction of bromide with sulfuric acid producing elemental sulfur

Steps:

• Oxidation state of sulfur in H₂SO₄ is +6 (from structure: S bonded to 4 O at -2 and 2 OH).
• Reaction products include Br₂ and elemental S when NaBr is warmed with conc. H₂SO₄.
• Sulfur reduces to oxidation state 0 in elemental S.
• Bromide ions (Br⁻, ox. state -1) oxidize to Br₂ (0), acting as reducing agent for sulfur.

Why B is correct:

• Bromide ions reduce sulfur from +6 to 0, matching the definition of a reducing agent as the species that donates electrons (Br⁻ → Br₂ + 2e⁻).

Why the others are wrong:

• A: Sulfur reduces to 0, not +4; bromide ions are reducing, not oxidizing agents.
• C: Sulfur starts at +6 in H₂SO₄, not +4; ignores initial oxidation state.
• D: Sulfur starts at +6, not +4; bromide ions are reducing, not oxidizing agents.

Final answer: B