Key steps in the Contact process for sulfuric acid

Steps:

• Burning sulfur in air (process 1) produces SO₂ as the initial step: S + O₂ → SO₂.
• SO₂ is catalytically oxidized to SO₃: 2SO₂ + O₂ → 2SO₃ (not listed but bridges to absorption).
• SO₃ reacts with water (process 4) to form H₂SO₄: SO₃ + H₂O → H₂SO₄ (done via oleum to avoid mist).
• Processes 2 and 3 are invalid: SO₂ dissolution in H₂SO₄ or water does not produce sulfuric acid.

Why C is correct:

• C pairs processes 1 and 4, matching the Contact process equations for SO₂ production and H₂SO₄ formation.

Why the others are wrong:

• A includes invalid process 2 (SO₂ in H₂SO₄ forms no key intermediate).
• B includes invalid process 3 (SO₂ in water forms H₂SO₃, sulfurous acid).
• D omits essential process 1 and includes invalid process 2.

Final answer: C