Assuming equal concentrations of conjugate base and acid, which one of the following mixtures is suitable for making a buffer solution with an optimum pH of 3.3 - 3.4?
a) NaOCI / HOCI (Ka = 3.2 x 10-8).
b) CH₃COO₂Na / CH₃COOH (Ka = 1.8 x 10-5)
c) NaCl / HCI
d) none of these
e) NH₃ / NH₄Cl (Ka = 5.6 x 10-10)
f) NaNO₂ / HNO₂ (Ka = 4.5 x 10-4)