Solution:

• Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products is manifested as either the release or the absorption of energy.
• At very high temperatures in the interior of the sun, protons fuse to form helium nuclei.
• This fusion process occurs inside the core of the Sun, and the transformation results in a release of energy that keeps the sun hot.