Which of these reactions is responsible for energy radiating from stars, including the sun?

Answer: Nuclear fusion reaction

The stars as well as sun is powered by nuclear fusion reactions. The nuclear fusion reaction is the one where two or more nuclei of atoms combine to form a single nucleus releasing enormous amount of energy. There are many Hydrogen nuclei present on the star that combine to form Helium. This is the main nuclear fusion taking place in various stars.

The reactions that occur are nuclear fision