Define the terms (i) mass defect, (ii) binding energy for a nucleus and state the relation between the two.
For a given nuclear reaction, the B.E./nucleon of the product nucleus/nuclei is more than that for the original nucleus/nuclei. Is this nuclear reaction exothermic or endothermic in nature? Justify your choice.

Explanation

(i) Mass defect `(Delta m),` of any nucleus `""_(Z)^(A) X` is the difference in the mass of the nucleus ( = M) and the sum of masses of its constituent nucleons ( = M.).
`therefore Delta m = M.-M`
`= [Zm_(p) + (A - Z) m_(n) ] -M`
where `m_(p) and m_(n)` denote the mass of the proton and the neutron respectively.
(ii) Binding energy is the energy required to separate a nucleus into its constituent nucleons. The relation between the two is
`"B. E." = ("mass defect") xx c^(2)`.
(iii) There is a release of energy i.e., the reaction is exothermic.
Reason : Increase in B.F/nucleon implies that more mass has been converted into energy. This would result in release of energy.