pH of mixtures of strong acid and strong base

2018 1 question

1. Following solutions were prepared by mixing different volumes of NaOH and HCl of different concentrations: a. 60 mL $\frac{M}{10}$ HCl + 40 mL $\frac{M}{10}$ NaOH; b. 55 mL $\frac{M}{10}$ HCl + 45 mL $\frac{M}{10}$ NaOH; c. 75 mL $\frac{M}{5}$ HCl + 25 mL $\frac{M}{5}$ NaOH; d. 100 mL $\frac{M}{10}$ HCl + 100 mL $\frac{M}{10}$ NaOH. pH of which one of them will be equal to 1?