At $27^{\circ} \mathrm{C}, 100 \mathrm{~mL}$ of 0.5 M HCl is mixed with 100 mL of 0.4 M NaOH solution. To this resultant solution, 800 mL of distilled water is added. What is the pH of final solution?

A solution is prepared by mixing 10 mL of 1.0 M acetic acid and 20 mL of 0.5 M sodium acetate and diluted to 100 mL . If the $\mathrm{p} K_a$ of acetic acid is 4.76, then the pH of the solution is