Question

Statement I : Nuclear fission is a spontaneous process i.e. there is no need of external energy supply for this to happen.
Statement II : In a nuclear fission reaction the rest mass energy of the parent nucleus is more than the combined rest mass energy of two daughter fragments and neutrons.

• A. Both the statements are correct and statement II infers to statement I
• B. Both the statements are correct but statement II doesn’t infer to statement I
• C. Statement I is correct but statement II is incorrect
• D. Statement II is correct but statement I is incorrect

Answer 1

The correct option is A Both the statements are correct and statement II infers to statement I

In a nuclear fission reaction a heavy nucleus breaks into two middleweight nuclei of comparable masses. Also the binding energy per nucleon of daughter nuclei is less than that of the parent nucleus. So, energetically the process is spontaneous.
Now the question is if we see the graph then can we conclude that any heavy weight nucleus will break into two relatively light weight nuclei and hence to decrease the binding energy?
The answer is no. Only unstable nuclei undergo fission. A stable nucleus may require energy to become unstable but once unstable it doesn't require any further energy to fission.

For example U-235 is a Uranium isotope which is relatively stable, but when bombarded with neutrons (This is how we supply energy to it) it absorbs it and becomes U-236. Now U-236 is a quite unstable nuclide and goes under fission spontaneously giving daughter nuclei with lesser rest mass energy.

Hence both the statements are correct and statement II infers statement I.