Buffre Solution and change in pH

What will be the pH if 0.01 mol of HCI is dissolved in the above buffer solution? Find the change in pH value.

The volume of water that must be added to 100 ml of NaOH solution to change its pH value from 12.6990 to 12 is

Buffre Solution illustration

Which solution will not show change in pH of dilution ?

Buffer capacity of a buffer solution is x , the volume of 1 M NaOH added to 100 mL of this solution if the change of pH by 1 is