Question

During a nuclear fission reaction:
This question has multiple correct options
A. A heavy nucleus breaks in two or more fragment by itself
B. A light nucleus bombarded by thermal neutrons breaks up
C. A heavy nucleus bombarded by thermal neutrons breaks up
D. Two light nuclei combine to give a heavier nucleus and possible other products

Answer 1

The nuclear fission reaction is the breakup of a nucleus into smaller nuclei. The mass of the new nuclei produced has a mass smaller than the parent nucleus.

Complete step by step answer:
The theory behind a nuclear fission is that a spontaneous splitting of an unstable atom occurs into two or more smaller particles which offer more stability. During a fission reaction energy is released. During the fission process extra neutrons are released which results in chain reaction.

There are various types of forces inside the nucleus which acts between the particles. The strong nuclear forces present inside the nucleons bind the protons and neutrons together inside the nucleus. The forces are strong because the nucleons are close together which results in the repulsion between like-charged protons. Thus there are two different forces which have opposite effect inside the nucleus. The strong nuclear force acts in bringing close the protons and neutrons. On the other hand the electromagnetic force pushes the protons apart.

The nuclear fission reaction is initiated by bombardment of high-energy neutrons. The neutron attacks the nucleus and produces a heavy atom which has a higher number of neutrons.

The element uranium $^{235}U$ undergoes a neutron bombardment to generate $^{236}U$. The $^{236}U$ is unstable and undergoes the fission process thereby releasing additional neutrons which further undergo a changing reaction by initiating other $^{235}U$ atoms.

In cases where nuclear fission occurs without bombardment of neutrons the process is called spontaneous fission. Hence option A and C are correct, i.e. during a nuclear fission reaction, a heavy nucleus breaks in two or more fragment by itself and a heavy nucleus bombarded by thermal neutrons breaks up

So, the correct answer is Option A,C.

Note: Heavier nucleus is obtained by neutron bombardment. The addition of an extra neutron to a nucleus results in a highly unstable nucleus due to different forces.