Collision Theory

Collision theory explains reaction rates by treating reactions as the outcome of molecular collisions, but it requires two conditions for a collision to be effective. First, the colliding molecules must possess kinetic energy equal to or greater than the activation energy so that bonds can be broken and rearranged. Second, the molecules must collide with the correct orientation so that the reactive parts come together properly. Because only a small fraction of collisions satisfy both the energy and the orientation requirements, only a few collisions per second lead to products, even though enormous numbers of collisions occur. The option that all collisions are too weak ignores the role of orientation. The option that molecules never collide contradicts kinetic theory entirely. The option that products decompose immediately confuses reversibility with collision effectiveness. This energy-and-orientation requirement, captured by the steric factor, is the NCERT basis of collision theory. Plausibility check: the activation-energy and orientation barriers together explain why measured rates are far smaller than the total collision frequency, confirming the chosen answer.