What happens to a star like our sun when it runs out of
hydrogen, explain the physical and chemical changes
that take place.

The core finally cools into a white dwarf, then a black dwarf. This is what happens when a normal-sized star dies. If a really huge star dies, it has so much mass that after the helium is used up, it still has enough carbon to fuse it into heavy elements like iron. When the core turns to iron, it no longer burns.

Explanation:

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements