Chlorine chemistry in acids, bases, and water

Steps:

• Analyze oxidation state changes in A using the reaction NaCl + H₂SO₄ → NaHSO₄ + HCl.
• Check products of B using Cl₂ + 2NaOH (cold) → NaCl + NaClO + H₂O and compare to hot conditions.
• Evaluate C using the equilibrium Cl₂ + H₂O ⇌ HCl + HOCl and its effect on pH.
• Note D lacks content for evaluation.

Why C is correct:

• Chlorine reacts with water via Cl₂ + H₂O ⇌ HCl + HOCl, releasing H⁺ from HCl to form an acidic solution.

Why the others are wrong:

• A: Chloride stays at -1 oxidation state in HCl; no oxidation occurs, as H₂SO₄ displaces but does not oxidize Cl⁻.
• B: Cold NaOH yields hypochlorite (Cl⁺¹), not full disproportionation to chlorate (Cl⁺⁵); that requires hot concentrated NaOH.
• D: Not enough information.

Final answer: C