Answer: When the rate of the forward reaction becomes equal to the rate of the backward reaction.
Explanation: Equilibrum system is a state of system in which all the species present are in equilibrium with each other.
Macroscopic properties are those which are larger in size and microscopic properties are those which are smaller in size.
Thus, macroscopic properties become constant in an equilibrium system when the rate at which the reactants are getting consumed is equal to the rate at which the products are getting produced. Thus this state of equilibrium is known as dynamic equilibrium.