(a) Explain the processes of nuclear fission and nuclear fusion by using the plot of binding energy per nucleon (BE/A) versus the mass number A.
(b) A radioactive isotope has a hald -life of 10 years. How long will it take for the activity to reduce to 3.125%.

Explanation

The point of (B.F/nucleon ) verses mass number is as shown

[Note : Also accept the diagram that just shows the general shapes of the graph ]
From the plot we note that
(i) During nuclear Fission
A heavy nucleus in the larger mass region (`A gt 200) ` breaks into two middle level nuclei , resulting in an increase in B.E/nucleon , this results in a release of energy.
(ii) During nuclear fussion
Light nucleus in the lower mass region `(A lt 20) ` fuse to form a nucleus having higher B.E/nucleon .Hence Energy gets released
[Alternatively -As per the plot :During nuclear Fission as well as nuclear fussion . the final value of B.E/nucleon is more than its intial value . Hence energy gets released in both these processes.]