∵ Concentration of NaOH(N1)=0.1N Volume of NaOH used (V1)=25mL Concentration of HCl(N2)=0.1N Volume of HCl(V2) used =V2 and ‌‌N1V1=N2V2 Thus, V2=‌
N1V1
N2
=‌
0.1×25
0.1
Volume of HCl used (V2)=25mL=V1 Thus, to convert 500mLHCl solution to 0.1NHCl, we need 500mL of water. Hence, option (b) is the correct answer.