Step-by-step explanation:
It is known that atomic mass is the sum of total number of protons and neutrons present in an element.
But when there occurs a difference in the mass of the nucleus of an atom and mass of its protons and mass of its neutrons then it is known as mass defect.
Basically, mass defect is the missing mass which is represented in the form of energy released upon formation of a nucleus.
Therefore, we can conclude that comparing the mass of the nucleus with the mass off the protons and mass of the neutrons refers to mass defect.