HX(aq) + H2O(l) → H3O+(aq) + X−(aq)
Based on the equation, HX would be classified as A) an acid, because it accepts a proton
B) a base, because it accepts a proton. C) a base, because it donates a proton D) an acid, because it donates a proton

The correct answer is option D.

Explanation:

According to the Bronsted-Lowry conjugate acid-base theory:

For the given chemical equation:

In the above reaction , is loosing a proton, thus it is considered as an acid and after losing a proton, it forms which is a conjugate base.

And, is gaining a proton, thus it is considered as a base and after gaining a proton, it forms which is a conjugate acid.

Hence,the correct answer is option D.