Help me with this physics question.

Question

A neutron and a proton combine to form a nucleus. Why does the mass of the nucleus differ from the sum of the masses of the individual nucleons?
A. The nucleus has less mass, because binding energy is converted into matter.

B. The nucleus has less mass, because matter is converted into binding energy.

C. The nucleus has more mass, because binding energy is converted into matter.

D. The nucleus has more mass, because matter is converted into binding energy.

Answer 1

When the nucleus is formed, the mass per nucleon decreases. The energy equivalent of the mass decrease, found with E=mc^2, is the binding energy.