Answer: The correct answer is option A.
Explanation:
There are 2 types of nuclear reactions:
1. Nuclear fission reaction: In this type of reaction, a heavier nuclei splits into two or more lighter nuclei. This process releases neutrons and further split additional atoms, generating into chain reactions.
[tex]A\rightarrow B+C[/tex]
where, A is heavier nuclei and B & C are lighter nuclei.
2. Nuclear fusion reactions: In this type, two lighter nuclei combines to form a single heavier nuclei.
[tex]A+B\rightarrow C[/tex]
where, A & B are lighter nuclei and C is a heavier nuclei.
In the given question, a heavier nuclei is splitting into two nuclei and releasing neutrons which are further splitting the two nuclei obtained into more nuclei. Hence, this is considered as a chain reaction which is caused by the splitting of nuclei or nuclear fission reaction.
Hence, the correct answer is Option A.
