What is the K_b for a base B, if the equilibrium concentrations are [B] = 1.48 , M, [HB⁻] = [OH⁻] = 3.13 × 10-4 , M?
a) 1.48 , M
b) 3.13 × 10-4 , M
c) 4.21 × 10-4
d) 7.05 × 10-8