Which of the following distinguishes a nuclear reaction from a chemical reaction? a. it involves atoms.
b. there is an exchange of electrons.
c. mass is conserved.
d. there is a change in the nucleus.

The option that distinguishes a nuclear reaction from a chemical reaction is D. there is a change in the nucleus.
During a nuclear reaction, two light nuclei combine in order to create a new, heavier one which is different than those two original ones and has additional particles that it didn't have originally. This is what makes the difference between these two reactions.