Nuclear fusion powers the Sun

Steps:

• Identify the Sun as a main-sequence star powered by nuclear reactions in its core.
• Recall that stars convert light elements into heavier ones to release energy.
• Distinguish fusion (combining nuclei) from fission (splitting nuclei).
• Match the process to hydrogen fusing into helium via the proton-proton chain.

Why C is correct:

• The proton-proton chain reaction fuses four hydrogen nuclei into one helium nucleus, releasing energy per E=mc² from mass defect.

Why the others are wrong:

• A: Fission splits heavy nuclei like uranium, not hydrogen, and doesn't occur in the Sun.
• B: Fusion combines light nuclei; helium fusing to hydrogen reverses the process and absorbs energy.
• D: Same as B; helium-to-hydrogen fusion is endothermic and not stellar power source.

Final answer: C