Nuclear binding energy is equivalent to 

CONCEPT:

• Binding energy (B.E.): The neutrons and protons in a stable nucleus are held together by nuclear forces and energy is needed to pull them infinitely apart (or the same energy is released during the formation of the nucleus). This energy is called the binding energy of the nucleus.
• The binding energy of a nucleus may be defined as the energy equivalent to the mass defect of the nucleus.

EXPLANATION:

• If Δm is a mass defect then according to Einstein's mass-energy relation

Binding energy = Δmc² = [{ m_pZ + m_n(A – Z)} – M ]c²

Where m_p = Mass of the proton, m_n = Mass of each neutron, M = Mass of the nucleus, Z = Atomic number, and A = Mass number

• (This binding energy is expressed in joule because Δm is measured in kg)
• From above it is clear that nuclear binding energy is equivalent to the mass defect of the nucleus. Thus option 4 is correct.