The phenomenon by which two light atomic nuclear combine to form a heavy nuclide with the release of energy is known as

Step 1: Analyze the question The question describes a process where two light nuclei join to form a heavier nucleus, releasing energy. The key words are "combine" and "light nuclei → heavy nuclide."

Step 2: Explain the concepts

• Radioactivity: the spontaneous disintegration of an unstable nucleus, emitting alpha, beta or gamma radiation. Nothing combines here.
• Nuclear fusion: two light nuclei join to form a heavier nucleus, releasing a large amount of energy. Example: two hydrogen isotopes (deuterium and tritium) fuse to form helium. ²H + ³H → ⁴He + ¹n + energy
• Nuclear fission: a heavy nucleus (e.g. Uranium-235) splits into two lighter nuclei when struck by a neutron, releasing energy. This is the opposite of fusion.
• Chain reaction: a self-sustaining series of fission events, where neutrons released by one fission trigger further fissions.

Step 3: Match the description "Two light nuclei combine to form a heavy nuclide with energy release" is exactly the definition of nuclear fusion. The energy comes from the mass defect (the products have slightly less mass than the reactants), given by E = Δm·c².

Step 4: Answer The correct option is B. nuclear fusion.

Exam tip: Remember: FUsion = FUse together (small → big), while FIssion = FIssure or split apart (big → small). Fusion powers the Sun and stars, while fission powers nuclear reactors and the original atomic bomb.