What process powers the Sun and involves the combination of light atomic nuclei?

The Sun is powered by nuclear fusion. In this process, light atomic nuclei, primarily hydrogen, combine under extreme temperature and pressure to form heavier nuclei, like helium, releasing a vast amount of energy.

The correct option is B.

• A- Fission: This is the splitting of heavy atomic nuclei, used in nuclear power plants on Earth.
• B- Fusion: This is the combining of light atomic nuclei, which powers the Sun and other stars.
• C- Endothermic: This describes a reaction that absorbs heat, which is not the primary energy-releasing process in the Sun.
• D- All of these: This is incorrect as only fusion powers the Sun.

The final answer is $\boxed{\text{B- Fusion}}$.