250 ML of a Hydrofluoric Acid Solution of Unknown Concentration

Multiple Choice

25.0 mL of a hydrofluoric acid solution of unknown concentration is titrated with 0.200 M NaOH. After 20.0 mL of the base solution has been added, the pH in the titration flask is 3.00. What was the concentration of the original hydrofluoric acid solution. [K_a(HF) = 7.1 * 10^-4]

A) 0.39 M
B) 0.27 M
C) 0.16 M
D) 2.4 M
E) 0.23 M