Name the nuclear fuel present in the sun.

The nuclear fusion of tiny nuclei in the sun generates its heat and light energy.

Nuclear fusion is the mechanism through which the sun and the majority of stars generate light and heat energy. Nuclear fusion is the process of combining many lighter nuclei into heavier ones, releasing a significant amount of energy in exchange for a relatively modest mass difference that results from the difference in the binding energies of the reactant and product nuclei.
Through the process of nuclear fusion, the sun transforms lighter hydrogen nuclei into heavier helium nuclei and releases a significant quantity of energy.
As a result, hydrogen, or more specifically, hydrogen nuclei, serves as the sun's nuclear fuel.

Hence, the correct answer is option C.