Neutralization data identifies SO₃ by matching molar mass

Steps:

• Moles of NaOH = 0.100 mol dm⁻³ × 0.025 dm³ = 0.00250 mol.
• SO₃ + H₂O → H₂SO₄, where H₂SO₄ + 2 NaOH → Na₂SO₄ + 2 H₂O (2 mol NaOH per mol SO₃).
• Moles of SO₃ = 0.00250 / 2 = 0.00125 mol.
• Molar mass = 0.100 g / 0.00125 mol = 80 g mol⁻¹ (matches SO₃).

Why D is correct:

• SO₃ (oxide of sulfur, Period 3) forms sulfuric acid with water; titration yields exact molar mass of 80 g mol⁻¹ per H₂SO₄'s diprotic nature.

Why the others are wrong:

• A. Al₂O₃: Amphoteric; forms neutral or slightly basic suspension with water, not acidic solution.
• B. MgO: Basic; forms Mg(OH)₂, giving alkaline solution.
• C. P₄O₁₀: Would produce 4 H₃PO₄ (12 mol NaOH per mol P₄O₁₀), requiring only 0.059 g for 0.00250 mol NaOH, not 0.100 g.

Final answer: D