In this task, you are given a question and answer options for that question. Using this information, you have to classify each text into different topics: medicine, nursery, psychology, chemistry, pharmacology, biology.
Q: Question: The molecularity of an elementary reaction corresponds:
Options: <0> At the initial concentration of reagent. <1> To the number of molecules that are found to react. <2> To the number of collisions of the reactants per unit of time. <3> At the final concentration of the product. <4> To the reaction between the reaction rate and the reagent concentration.
A:
pharmacology