25.0 cm³ of 0.200 mol/dm³ sodium hydroxide solution is exactly neutralised by 20.0 cm³ of sulphuric acid solution. What is the concentration of the sulphuric acid? [Equation: $2NaOH + H_2SO_4 \rightarrow Na_2SO_4 + 2H_2O$]

Moles of NaOH = (25.0/1000) × 0.200 = 0.005 mol. From the equation, moles of H₂SO₄ = 0.005/2 = 0.0025 mol. Concentration of H₂SO₄ = 0.0025/(20.0/1000) = 0.0025/0.020 = 0.125 mol/dm³. Option A ignores the 2:1 mole ratio, option C results from a volume ratio error, and option D uses the NaOH concentration directly.