Which of the Following Mixtures Gives a Buffer with a PH

Multiple Choice

Which of the following mixtures gives a buffer with a pH less than 7.0? For acetic acid, K_a = 1.8 * 10^-5 and for NH₃,K_b = 1.8 *10 ^-5.

A) 10 mL of 0.1 M NH₃(aq) + 10 ml of 0.1 M HCl(aq)
B) 10 mL of 0.1 M aqueous acetic acid + 5.0 mL of 0.1 M NaOH(aq)
C) 10 mL of 0.1 M aqueous acetic acid + 10 mL of 0.1 M NaOH(aq)
D) 10 mL of 0.1 M aqueous acetic acid + 10 mL 0f 0.1 M NH₃(aq)
E) 10 mL of 0.1 M NH₃(aq) + 5.0 mL of 0.1 M HCl(aq)