A buffer may be prepared by mixing a weak acid with a certain amount of strong base. Which of the acids best for preparation of a buffer with pH of 7.00
a. ammonium ;Ka=5.6x10^-10
b. formic acid;Ka=1.9X10^-4
c. benzoic acid;Ka=6.6x10^-5
d. dihydrogen phosphate ion;Ka=6.2x10^-8
Answer: d