Comparing the mass of the nucleus with the mass of the protons and the mass of the neutrons refers to what?
einstein’s theory of relativity
nuclear binding energy
the weak force
the strong force
mass defect

The best option in here is the mass defect. This is so because the mass defect is the difference between the particles of the nucleous weight and the nucleous itself. According to the equation E=mc^2, the mass defect is related the the binding theory. In order to calculate the mass defect of an atom you need to add up the masses of each proton and each of neutron that are present in the nucleus and then you substract the actual mass of the nucleus from the combined mass. That is why in mass defect you need the information given in your question. 

The correct answer is d