Following four solutions are prepared by mixing different volumes of NaOH and HCl of different concentrations, pH of which one of them will be equal to 1 ?
100 mL ${M \over {10}}$ HCl + 100 mL ${M \over {10}}$ NaOH
75 mL ${M \over {5}}$ HCl + 25 mL ${M \over {5}}$ NaOH
60 mL ${M \over {10}}$ HCl + 40 mL ${M \over {10}}$ NaOH
55 mL ${M \over {10}}$ HCl + 45 mL ${M \over {10}}$ NaOH
