18.Activated complex is formed due to

Explanation

The correct answer for the formation of an activated complex is:(b) Effective collisionsHere's why the other options are incorrect:(a) Pressure: While pressure can indirectly influence the frequency of collisions by increasing the concentration of reactants, it's not the direct cause of forming the activated complex. The specific arrangement and energy exchange during a collision determine the formation of the transition state.(c) Ineffective collisions: These collisions happen between reactant molecules but lack the necessary energy or orientation to overcome the activation energy barrier and proceed to the product state. They don't lead to the formation of the activated complex.(d) Temperature: While temperature affects the frequency of collisions and provides the kinetic energy needed for reactions, it's not the immediate reason for an activated complex to form. The specific interaction and energy configuration of participating molecules during a collision dictate its transition to the activated state.