Why the mass of the nucleus is less than the sum of masses of the nucleons?

The mass of an atomic nucleus is less than the sum of the masses of its constituents. Thus mass defect is converted in to

Which of the following statement (s) is/are correct (i) The rest mass of a stable nucleus is less than the sum of the rest masses of its separated nucleous (ii) The rest mass of a stable nucleus is greater than the sum of the rest masses of its separated nucleous (iii) In culear fusion, energy is released by fusion two nuclei of medium amss (approximaltely 100 "amu" ) (iv) In nuclear fussion, energy is released by freagmentation of a very heavy nucleus

The mass of a ._(3)^(7) Li nucleus is 0.042 u less than the sum of the masses of all its nucleons. The binding energy per nucleon of ._(3)^(7)Li nucleus is nearly

The mass of a a_3^7 Li nucleus is 0.042 u less than the sum of the masses of all its nucleons. The binding energy per nucleon of ._3^7 Li nucleus is nearly.

The mass number of a nucleus is