Hydrogen Fusion Powers Stable Stars

Steps:

• Stable stars maintain energy output through core nuclear reactions converting mass to energy.
• The dominant process fuses light elements to heavier ones, releasing vast energy.
• In main-sequence stars like the Sun, hydrogen atoms combine via the proton-proton chain.
• This forms helium, matching option D as the primary reaction.

Why D is correct:

• The proton-proton chain fuses four hydrogen-1 nuclei (protons) into one helium-4 nucleus, with two positrons and neutrinos, following E=mc² where mass defect converts to energy sustaining stellar stability.

Why the others are wrong:

• A: Fission splits heavy nuclei like uranium, not helium into lighter hydrogen; stars fuse, not split.
• B: Fusion builds heavier elements from lighter ones; helium fusing to hydrogen reverses this impossible process.
• C: Similar to B, helium fusion produces heavier elements like carbon, not lighter hydrogen.

Final answer: D