Which of the following buffers will have the lowest pH?
a. a solution containing 0.20 M HC2H3O2 and 0.20 M NaC2H3O2
b. a solution containing 0.25 M HC2H3O2 and 0.15 M NaC2H3O2
c. a solution containing 0.15 M HC2H3O2 and 0.25 M NaC2H3O2
d. they all have the same pH