Answer: Option (A) is the correct answer.
Explanation:
A reaction in which nucleus of an atom and a subatomic particle like proton or neutron collide or when any two nuclei combine together then it results in the formation of a new nucleus that is different from its parent nuclei.
For example, [tex]^{235}U + n \rightarrow ^{134}Xe + ^{100}Sr + 2n[/tex]
Here, nucleus of Uranium collides with a neutron resulting in formation of a Xenon and Strontium nucleus along with two neutrons.
Therefore, we can conclude that nuclei of an atom participates in the given reaction.