Answer:
Substance X will rise due to convection.
Explanation:
The most fundamental property of a star that determines its evolution is the MASS of the star.
In fact, while low-mass stars usually end their life becoming red giants and then white or black dwarfs, the high-mass stars can evolve into red supergiants and eventually originate a supernova. After the explosion of the supernova, depending on their mass, they can becomes neutron stars or collapse into black holes.
Natural sources of light include our sun and other stars, where the source of energy is nuclear energy (recall that the moon does not produce light but merely reflects sunlight), lightning, where the source is electrical, and fire, where the energy source is chemical.