Which best describes thermal energy? It is the difference between internal energies of two or more substances. It is the sum of
internal energies of two or more substances. It is the portion of internal energy that can be transferred from one substance to another. It is the portion of potential energy that can be transferred from one substance to another.
The answer to your proposed question is Neutron. This is because the atomic mass unit of a neutron is 1 and so it would contribute to the overall mass of the atom. I hope this answer helped you!