The common-ion effect is a consequence of
a. boyle s law.
c. avogadro s principle.
b. le ch telier s principle.
d. chemical kinetics.

The answer is the option b. Le Chatelier's principle.

Le Chatelier's principle states that when chemical equilibrium is taken out of the equilibrium the reaction will shift to restore the equilibrium. 

The common-ion efect is the addition of a solution that apports an ion that is already in the solution, which then will shift the reaction to reach a new equillibrium.