The mass of a nucleus is less than the total mass of its nucleons. this difference in mass indicates that some of the mass has been converted intoheatbinding energyphotoelectric effectradioactivity

Option B , Binding Energy

Explanation:

The energy in combining two nucleus is lost in binding them. This binding energy is too large that it causes significant loss of mass and is calculated using the Einstein’s theory of relativity.  

When two nucleons combine , mass defect is caused which leads to loss of mass associated with energy and therefore the mass of nucleus is less than the mass of nucleons.  

Hence, Option B is correct.

your answer should be c) enjoy!