Final answer:
Nuclear fusion in medium-sized stars primarily involves the fusing of hydrogen isotopes to form helium and other medium-mass nuclei, releasing significant energy in the process.
Step-by-step explanation:
In medium-sized stars, nuclear fusion refers to the process where two light atomic nuclei combine to form a heavier nucleus. This fusion process is essentially the fusing of hydrogen isotopes to form helium and other medium-mass nuclei. The most prevalent fusion process in stars is the proton-proton cycle, which involves the fusion of four protons (hydrogen nuclei) into one alpha particle (helium nucleus), along with the release of positrons, neutrinos, and a significant amount of energy. An example of this is the reaction where deuterium (²H) and tritium (³H) combine to create helium (⁴He) and release energy alongside a free neutron.