Final answer:
Le Châtelier's Principle explains the common ion effect through a change in equilibrium.
Step-by-step explanation:
Le Châtelier's Principle explains the common ion effect through a change in equilibrium. When a common ion is added to a weak acid or weak base equilibrium, the equilibrium will shift towards the reactants. This is because the presence of the common ion decreases the solubility of an ionic species or the ionization of a weak acid or base, according to the common ion effect.