The mass of a nucleus is less than the total mass of it's nucleons. this difference in mass indicates that some of the mass has been converted into

Some of the mass gets converted in the form of energy related to mass.

Explanation:

Mass defect is defined as the difference in the mass of an isotope and the mass number of an atom. Equation representing mass defect is:

where,

= mass defect of an atom

= number of protons

= mass of one proton

= number of neutrons

= mass of one neutron

M = mass number

The mass number of an atom (mass of nucleus) is always less than the isotopic mass (total mass of its nucleons) because energy is released when nucleus gets formed. This energy is related to mass of the nucleus and is known as binding energy.

Hence, some of the mass gets converted in the form of energy related to mass.