Answer and explanation:
A correct option is an option (A). A control fission reaction occurs in the nuclear reactor. Neutrons are bombarded with radioactive nuclei, and the fission process triggers. This fission process is a chain reaction and is required to be controlled. In nuclear fission, the atomic nuclei undergo a fission process and in the process, the energy is released. The reaction is controlled by using control rods that absorb the neutron.
Option B is incorrect because acid-base reactions are usually encountered in chemistry.
Option C is incorrect because the reactor technology that we are using today is based on nuclear fission and not on nuclear fusion. In nuclear fusion, two atomic nuclei are fused and the energy is released in the process.
Option D is also incorrect because the reaction in nuclear reactors is controlled nuclear fission.