Nuclear fission is the splitting of nucleus of an atom which results in the emission of high amount of energy.
<u>Example:</u>
Heavy atom (i.e. uranium) when bombarded with neutrons, its nucleus split into smaller lighter weight nuclei and release a huge amount of energy. (Nuclear fission also takes place without neutrons i.e. in the form of radioactive decay (the process in which an unstable nucleus of an atom releases energy in the form of radiation)).
