Which One of These Combinations Would Give a Buffer That

Multiple Choice

Which one of these combinations would give a buffer that would be most effective in the pH range 3.0 tO₄.0?

A) 0.10 M CH₃COOH, 0.10 M CH₃COONa, K _a = 1.8×10 ^{- 5}
B) 0.10 M NH₄Cl, 0.10 M NH₃, K _b = 1.8×10 ^{- 5}
C) 0.10 M HF, 0.10 M NaF, K _a = 3.54×10 ^{- 4}
D) 0.10 M H₂CO₃, 0.10 M NaHCO₃, K _a = 4.30×10 ^{- 7}
E) 0.10 M HCl, 0.10 NaCl