4g = 0.1 mols of NaOH
Molarity =0.1mols0.1L=1M
According to the equation:
N1V1=N2V2
M1V1=M2V2 (∵H2SO4 is a diprotic acid)
1M×0.1=2.5×2×V2
=0.15=0.02L=20mL