Answer. According to Law of mass action, rate of a reaction is directly proportional to active mass i.e., rate is high if concentration is high or rate is low if concentration is low. With the passage of time, the concentration of reactants decreases, while the concentration of products increases. So, forward reaction rate decreases while reverse reaction rate increases. Ultimately, when equilibrium stage approaches the forward reaction rate slow down because its concentration has decreased. As, at equilibrium state the reverse reaction rate is equal to forward reaction rate hence, both reaction rate takes place slowly as shown in graph.