Concept:Fusion combines light nuclei, such as hydrogen protons, into a heavier helium nucleus and releases enormous energy.
Explanation:In the Sun and other stars, extreme temperature and pressure force protons to overcome their electrical repulsion.
Four hydrogen nuclei undergo a chain of reactions to form one helium nucleus:
411H→24He+2β++energy.
This is a nuclear fusion reaction.
Because it occurs at extremely high temperatures, it is specifically called thermonuclear fusion.
Thermionic emission involves heat-induced electron flow, nuclear fission splits heavy nuclei, and photoelectric emission releases electrons when light strikes a material.
None of these describe the conversion of protons into helium with a tremendous energy release.
Answer:C. thermonuclear fusion