The acid-dissociation constant, Ka, for benzoic acid is 6.5 × 10-5.

Calculate the base-dissociation constant, Kb, for the conjugate base of benzoic acid.

A. 9.3 × 105

B. 2.5 × 10-6

C. 6.5 × 109

D. 1.5 × 10-10