Option A. The reaction would shift to balance the change.
Explanation:
According to Le Chatelier's principle, if an external constrain such as change in concentration, temperature or pressure is imposed on a chemical system in equilibrium, the equilibrium will shift in order to neutralize the effect.
If the equilibrium of a weak acid dissociation reaction is upset, the equilibrium will shift to balance the change as explained by Le Chatelier's principle.
