Final answer:
The reason for the abundance of hydrogen in Jupiter's interior is most likely because Jupiter formed from the gravitational contraction of hydrogen gas. This process allowed Jupiter to have a similar cosmic composition to the early Solar System. The heat in its interior is mainly primordial heat, remaining from its formation, and not due to nuclear fission.
Step-by-step explanation:
The vast amount of hydrogen in the interior of Jupiter is likely because Jupiter formed from the initial gravitational contraction of hydrogen gas. The collapse of gas from the nebula during the formation of the giant planets, which involved accreting nearly the same hydrogen-rich composition as the Sun, applies most efficiently to Jupiter (and Saturn), giving them a composition most nearly "cosmic" or similar to the original composition of the early Solar System. As such, hypothesis C) is the most accurate. Statements about nuclear fission and the melting down of atoms to hydrogen are not supported by scientific observations or theories related to planetary formation.
Jupiter has a huge internal energy source that can be attributed to primordial heat remaining from the formation of the planet. This heat contributes to raising the temperatures in Jupiter's interior higher than would be expected by solar heating alone. Due to its large mass and the pressure in its interior, the hydrogen in Jupiter exists mainly in a liquid metallic state, which is crucial for understanding the planet's overall magnetic and thermal properties.