SO₂ neutralization with Ca(OH)₂ forms CaSO₄ in aqueous solution

Steps:

• SO₂ dissolves in water, forming H₂SO₃, which acts as a weak acid.
• In aqueous solution with dissolved oxygen, H₂SO₃ oxidizes to H₂SO₄.
• H₂SO₄ reacts with Ca(OH)₂ via neutralization: H₂SO₄ + Ca(OH)₂ → CaSO₄ + 2H₂O.
• CaSO₄ precipitates as the main initial solid product.

Why C is correct:

• CaSO₄ forms directly from the oxidation and acid-base reaction, per standard flue gas desulfurization chemistry.

Why the others are wrong:

• A. Ca(SO₃)₂ uses incorrect formula (calcium sulfite is CaSO₃) and represents unstable intermediate.
• B. CaS forms from H₂S reactions, not SO₂.
• D. SO₃ is a gaseous intermediate in SO₂ oxidation but not a product here.

Final answer: C