Which of the Following Solutions Will Be the Best Buffer

Multiple Choice

Which of the following solutions will be the best buffer at a pH of 9.26? (K_a for HC₂H₃O₂ is 1.8 × 10^-5; K_b for NH₃ is 1.8 × 10^-5.)

A) 0.20M NH₃ and 0.20M NH₄Cl
B) 5.0M HC₂H₃O₂ and 5.0M NH₄Cl
C) 0.20M HC₂H₃O₂ and 0.20M NaC₂H₃O₂
D) 5.0M NH₃ and 5.0M NH₄Cl
E) 5.0M HC₂H₃O₂ and 5.0M NH₃