Answer: letter C ("Simply rearrange during the reaction to form new molecules").
Step-by-step explanation:
The question requires us to choose, among the options given, which one correctly represents what happens to atoms when they participate in a chemical reaction.
A chemical reaction involves the breaking of bonds between the reactants molecules (or particles) and the formation of new bonds to obtain the products.
In a balanced chemical reaction, the number of atoms in reactants and products is the same, thus we can affirm that the atoms that exist in the beginning of the reaction are not lost or transformed in completely new atoms. Although a chemical reaction may release energy, this energy is the result of breaking and forming new bonds.
A catalyst is a substance that is able to increase the rate of the reaction without taking part in the process of the reaction (the catalyst should not go through any permanent change during the reaction). Therefore, the catalyst is not able to replace atoms in the chemical reaction.
Considering what happens in a chemical reaction, we can say that the atoms present at the beginning of the reaction are rearranged in order to yield the products of the reaction.
Therefore, considering the information above, the best option to answer the question is letter C ("Simply rearrange during the reaction to form new molecules").