According to activated complex theory, the rate of a reaction depends on: (a) the intensity of collision (b) initial velocity of molecules (c) energy of activation of the molecules (d) the velocity of molecules with which they cross the energy barrier.

The Activated Complex Theory, also known as Transition State Theory, explains the rate of a chemical reaction. According to this theory, for a reaction to occur, the reacting molecules form an ‘activated complex’ or ‘transition state’ at the peak of the potential energy barrier. This complex is both formed and decomposed to give product molecules.

According to this theory, the rate of a reaction depends on how often the molecules collide (collision frequency), the orientation of the reacting molecules at collision, and the energy of the colliding molecules (they should have energy greater than or equal to the activation energy). Therefore, we can say that (a) the intensity of collision (or collision frequency), (c) the activation energy of the molecules and (d) the velocity of molecules with which they cross the energy barrier (related to their energy content) are all factors affecting the rate of reaction according to the Activated Complex Theory. However, (b) the initial velocity of the molecules is not a direct factor influencing the rate of reaction according to this theory.

So, options (a), (c) and (d) are correct. Option (b) is not directly a factor influencing the rate of reaction according to the Activated Complex Theory.