Why are inner planets so dense?

What is the Sun made of?

Name the following:

The celestial bodies that revolve around the sun between the orbits of Mars and Jupiter.

Name the following:

The planet that is least dense among all planets of solar system.

Name the following:

The unburnt meteoroids that reach the earth's surface.

Name the following.

The only planet that supports life: ______

Name the following:

The outer planet with a retrograde motion.