400 mL
H2SO4的物质的量 = 2 mol/L × 100/1000 L = 0.2 mol
设需要NaOH的物质的量是x
H2SO4 + 2 NaOH = Na2SO4 + 2 H2O
0.2 mol x
x = 0.4 mol
所以需要 0.4 ÷ 1 = 0.4 L = 400 mL 1 mol/L的NaOH溶液