(a) Rate of forward reaction is equal to rate of backward reaction at equilibrium.
(b) Aftere reaching the chemical equilibrium, the concentrations of reactants and product remain unchanged with time.
(c) For A (g) $\rightleftharpoons$ B(g), $K_c$ is $10^{-2}$. If this reaction is carrird out in the presence of catalyst, the value of $K_c$ decreases
(d) After reaching the equilibrium,both forward and backward reactions continue to take place.
