Why molecularity is applicable only for elementary reactions and order is applicable for elementary as well as complex reactions?

Explanation

As we know, elementary reactions proceed in single step while complex reactions generally take place in many steps. In multiple step reactions, each step has its own moleculairty and the molecularities of these steps are not added up. Therefore, complex reactions have no molecularity. On the other hand, in a complex reaction the order as determined for that slowest step, also called rate determining step, represents the order for the entier reactions. Hence, we may molecularity is applicable only to the single step reactions whereas order applies to both elementary and complex reactions.