Define the following terms:
$(a)$ Activation energy
$(b)$ Activated complex

(N/A) Activation energy: It is the minimum extra amount of energy absorbed by the reactant molecules so that their energy becomes equal to the threshold value,enabling them to undergo a chemical reaction.
$(b)$ Activated complex: It is an unstable intermediate species formed during the course of a chemical reaction,where the bonds of the reactants are partially broken and the bonds of the products are partially formed. It corresponds to the energy maximum on the potential energy profile.