Excitation and relaxation of electrons in what element are responsible for most of the light reaching Earth from the Sun? A) Argon B) Helium C) Hydrogen D) Iron

The answer here is B: Helium.

As many stars, the sun is largely composed of hydrogen and helium. The sun is able to give off radiant energy through the nuclear fusion process. This involves the process by which hydrogen isotopes fuses to create one helium atom and then creates radiant energy that travels to Earth.