Water will react most completely as an acid with

A. SO3^-2
B. H2BO3-
C. C6H5O-
D. CH3COO-

Why isn't the answer A, since
H2O + SO3^-2 <-> HSO3- + OH-
so H2O and HSO3- are the conjugate acids.

4 answers

What you say is true but that isn't the question. A, B, C, AND D (ALL OF THEM) are bases and ALL will react with H2O to produce acids. The question is which ONE does this more completely.
Oh, so they're all bases. Is the answer C because it is the strongest base out of the four. Does the stronger the base mean the more reaction? Thanks.
I can't read the small number in my text but it appears that phenol (C6H5OH) is the smallest which would make Kb the largest. What it means is, we write the equilibrium for the reaction with water as
A^- + HOH ==> HA + OH^-

Kb = Kw/Ka = (HA)(OH^-)/(HA)
So a large Kb means HA and OH are large and HA is small and that means the reaction occurs to a larger extent than for a small Kb. (Remember the discussions you have had about the reaction quotient).
Thank you so much for the clarification!