Which of the following statements about buffers is true?
Select one:
a. A buffer composed of a weak acid of pKa = 5 is stronger at pH 4 than at pH 6.
b. At pH values lower than the pKa, the salt concentration is higher than that of the acid.
c. The pH of a buffered solution remains constant no matter how much acid or base is added to the solution.
d. The strongest buffers are those composed of strong acids and strong bases.
e. When pH = pKa, the weak acid and salt concentrations in a buffer are equal.