Which of the following acids has the weakest conjugate base?
a. benzoic acid, ka = 6.31 x 10-5
b. ascorbic acid, pka = 4.1
c. 3-chlorobenzoic acid, pka = 3.8
d. chloroacetic acid, ka = 1.26 x 10-3
e. 2-hydroxybenzoic acid, pka = 3.0

Conjugate base of chloroacetic acid will be weakest.

Explanation:

of an acid is a parameter to predict it's acidic strength.

Higher the , higher will be acid dissociation . Hence acidity will be higher.

We know that the stronger an acid, the weaker it's conjugate base. So higher the value of an acid, weaker will be it's conjugate base.

The order of value:

So, conjugate base of chloroacetic acid will be weakest.

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).