Question

Which of the following Ka values represents the acid with the strongest conjugate base?

Answer 1

You could simply note that the conjugate base has a `K_b` such that

`K_w = K_aK_b`

where `K_b` is the base association constant and `K_w` is the water autodissociation constant.

Therefore,

`K_b = K_w/K_a`

The smaller the `K_a`, the larger `K_w/K_a` will be, and thus the larger `K_b` will be, making it the stronger conjugate base.

In other words, the weaker the acid, the stronger the conjugate base, i.e. the more the acid wants to keep its proton, the more its conjugate base will want the proton back.