Which statement describes nuclear fission?

• A. A nucleus absorbs a neutron and becomes heavier without releasing energy.
• B. A nuclear reaction in which a massive nucleus splits into smaller nuclei with the simultaneous release of energy
• C. A reaction where two light nuclei combine to form a heavier nucleus
• D. The emission of gamma rays from a nucleus.

Answer: (B)

Nuclear fission is the process in which a heavy nucleus splits into two (usually) lighter nuclei, releasing a large amount of energy in the process. This energy comes from the binding energy difference: the total mass of the products is less than the original mass, and that missing mass appears as energy (E = mc^2). The reaction often emits neutrons as well, which can trigger further fission events in a chain reaction—crucial for reactors and weapons. This description matches the statement that a massive nucleus splits into smaller nuclei with simultaneous release of energy. The other scenarios describe neutron capture with no energy release, fusion of light nuclei, or gamma decay, which are different processes.