Assuming Equal Concentrations of Conjugate Base and Acid, Which One

Multiple Choice

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 4.6-4.8

A) CH₃COO₂Na / CH₃COOH (K_a = 1.8 * 10^-5)
B) NH₃ / NH₄Cl (K_a = 5.6 *10^-10)
C) NaOCl / HOCl (K_a = 3.2 * 10^-8)
D) NaNO₂ / HNO₂ (K_a = 4.5 * 10^-4)
E) NaCl / HCl