Which process powers stars by fusing light nuclei?

• A. Fission
• B. Fusion
• C. Radioactive decay
• D. Spontaneous emission

Answer: (B)

Fusion powers stars because light nuclei combine to form heavier ones, and the resulting nucleus has a higher binding energy per nucleon. When hydrogen nuclei fuse to helium in stellar cores, some of the mass is converted to energy (mass defect), released as gamma rays, neutrinos, and kinetic energy of particles. The extreme temperatures and pressures in the core allow nuclei to overcome their electrostatic repulsion long enough for fusion to occur, sustaining the star’s luminosity and pressure balance. Other processes like fission split heavy nuclei, radioactive decay releases energy more slowly and isn't the sustained power source in stars, and spontaneous emission involves photons emitted from excited states rather than a continuous energy generation mechanism.