Answer: A. Catalyst
Explanation: A chemical reaction is a reaction between reactants which, due to different chemical processes during the reaction, yields a particular reaction product. A catalyst is a compound or substance that does not participate in the process as a reactant, therefore it does not affect the chemical composition of the compound obtained by the reaction, but only serves to speed up the chemical process. So the catalyst is not part of the chemical process as a reactant or product, just as a mechanism for faster reaction.
