Which of the Following Will Give a Buffer with a PH

Multiple Choice

Which of the following will give a buffer with a pH near 9.24 when the acid and conjugate base are mixed in equimolar proportions?
Acid
K_a
NH₄⁺ (from ammonia)
5) 69 × 10^-10
HC₂H₃O₂ (acetic acid)
1) 75 × 10^-5
HF (hydrofluoric acid)
6) 8 × 10^-4
CH₃CH₂NH₃⁺ (from ethylamine)
2) 12 × 10^-11

A) ammonia
B) acetic acid
C) hydrofluoric acid
D) ethylamine
E) none