Stoichiometry of acid-base reactions determines NaOH volumes Steps:

• Moles of H₂SO₄ used for each sample: 50 cm³ × 1 mol dm⁻³ = 0.05 mol.
• For NaHSO₄ (1:1 NaOH:H₂SO₄ ratio): 0.05 mol NaOH required.
• For Na₂SO₄ (2:1 NaOH:H₂SO₄ ratio): 0.10 mol NaOH required.
• With 2 mol dm⁻³ NaOH, volumes are 0.05/2 = 25 cm³ (NaHSO₄) and 0.10/2 = 50 cm³ (Na₂SO₄).

Why A is correct:

• Matches 25 cm³ for NaHSO₄ and 50 cm³ for Na₂SO₄ per the 1:1 and 2:1 molar ratios.

Why the others are wrong:

• B: 12.5 cm³ underestimates NaOH for Na₂SO₄ (ignores 2:1 ratio).
• C: Reverses volumes, assigning 50 cm³ to NaHSO₄ (should be 1:1, not 2:1).
• D: Identical to C, incorrect reversal of volumes.

Final answer: A