ANS:A - nuclear fission

Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into two or more smaller nuclei, along with the release of a large amount of energy. This process usually occurs when a heavy atomic nucleus, such as uranium-235 or plutonium-239, absorbs a neutron, becoming unstable and splitting into smaller fragments, or fission products. This reaction releases additional neutrons, which can then go on to induce further fission reactions in nearby nuclei, leading to a self-sustaining chain reaction. The energy released during nuclear fission is immense and is the basis for the destructive power of nuclear weapons such as atom bombs.