Answer: The correct answer is Option d.
Step-by-step explanation:
Nuclear fission reaction is defined as the reaction in which 1 heavier nuclei splits into two or more smaller nuclei.
As, nuclear fission reactors require a large amount of energy to split the nucleus, hence it is bombarded with a particle in order to star the reaction.
In a nuclear reaction, a large fissile atomic nucleus like Uranium-235
or Plutonium-239
when absorbs a neutron, it undergoes nuclear fission reaction.
Hence, in the given options, uranium-235 is absorbing a neutron. Therefore, the correct answer is Option d.