What causes a star to shine brightly?

The correct answer is the energy that is released.  

As the stars are tremendously hot, they shine. The source of their energy is nuclear fusion reactions taking place deep within the stars. In the majority of the stars, like the Sun, hydrogen is getting transformed into helium, a procedure that radiates energy, thus, heating the star and making it bright. Thus, the reaction known as nuclear fusion emits energy that makes the star to shine brightly.  

The energy that is released

Explanation:

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

50.23 i believe is correct but don't quote me on that.