Which of the following are present both before and after a chemical reaction?
a. reactants
b. catalysts
c. activation energy
d. products

Catalysts is wrong because it is never in the chemical equation. It only speeds up the reactions. A is wrong because reactants are only before the chemical reaction. D is wrong because products are only after the chemical reaction. It's C because the energy is still in the molecules and is not lost when it goes through the chemical reaction. Hope this helps! ;)

500bc indiais the answer.

Answer) by studying proton collisions hope this : )