Concept:The energy needed to split a nucleus into its individual protons and neutrons is its binding energy.Explanation:The nucleus is held together by the strong nuclear force.To separate it completely into isolated protons and neutrons, a definite amount of energy must be supplied.This required energy is called the nuclear binding energy.It is not the mass defect, which measures the mass difference, nor electron binding energy or excitation energy.Answer:D. nuclear binding energy