The source of the Sun’s energy is the process of
(1) Photoelectric emission
(2) Nuclear fission
(3) Nuclear fusion
(4) Thermionic emission
Answer: (3) Nuclear fusion is a nuclear reaction in which two or more atomic nuclei join together, or “fuse”, to form a single heavier nucleus. During this process, the matter is not conserved because some of the mass of the fusing nuclei is converted to energy which is released. Fusion is the process that powers active stars. The fusion of two nuclei with lower masses than iron (which, along with nickel, has the largest binding energy per nucleon) generally releases energy, while the fusion of nuclei heavier than iron absorbs energy. Fusion generally occurs for lighter elements only, and likewise, that fission normally occurs only for heavier elements.
