For a solution in which both an acid and base are present, the forward and reverse rates of proton transfer will:.a. always be equal. b. never be equal.
c. be equal once equilibrium is reached.
d. depends on the acid and base.

be equal once equilibrium is reached.

Explanation:

Given an equilibrium proton transfer such as the one written below;

HA + :B ⇄ HB + :A

The rate of forward reaction and the rate of reverse reaction becomes equal at equilibrium.

To put it in another way, at equilibrium, the rate of forward and reverse rates of proton transfer will  be equal.

oxygen, selenium, tellurium, and polonium.

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