the balanced equation for the reaction between NaOH and HCl is as follows
NaOH + HCl ---> NaCl + H₂O
stoichiometry of NaOH to HCl is 1:1
number of NaOH moles reacted - 0.250 mol/L x 0.0200 L = 0.005 mol
therefore number of HCl moles reacted - 0.005 mol
molarity of given HCl solution - 0.100 M
number of HCl moles in 1 L - 0.100 mol
then 0.005 mol of HCl in - 0.005 mol / 0.100 mol/L = 50.0 mL
volume of HCl required is 50.0 mL
