The Acid- Dissociation Constant, K_a, for Gallic Acid Is 4

The acid- dissociation constant, K_a, for gallic acid is 4.57 × 10^{- 3}. What is the base- dissociation constant, K_b, for the gallate ion?

A) 7.81 × 10^{- 6}
B) 5.43 × 10^{- 5}
C) 2.19 × 10^{- 12}
D) 2.19 × 10²
E) 4.57 × 10^{- 3}