You run an experiment to determine the buffer capacity of a 0.50 M acetic acid/acetate buffer. You use 22.87 mL of 0.0878 M KOH to titrate 10.00 mL of the buffer solution and effect a change of 1.02 pH units. What is the buffer capacity of the buffer in question?

I think that this site is very instructive.

Buffer capacity (http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity)

When the buffer capacity become highest?

When do you think it will become highest? State your opinion and try to support it.

That's what's the charm in science, as long as you can support your claim, you will be fine :)