Concept:Collision theory explains how chemical reactions occur and why reaction rates differ.
Explanation:Collision theory states that reactant particles must collide before a reaction can take place.
Not every collision produces a reaction; only effective collisions with sufficient energy and correct orientation lead to products.
The reaction rate therefore depends on how frequently the reactant particles collide.
This means the key factor is the frequency of collision of the reactants.
Increasing concentration, pressure, or temperature raises this collision frequency and speeds up the reaction.
The size of the reactants or products is not the main factor, and product collisions are not used to explain the rate.
Answer:B — frequency of collision of the reactants.