Density describes how much mass is contained in a certain volume. knowing how far apart molecules are in each state, which best ranks solids, liquids, and gasses from least dense to most dense?

Generally the order is for materials of a single molecule
Gasses are the least dense
Liquids are in between
Solids are the most dense

as evident if you pour sand in a cup of water, the least dense air (gas) will float on top, and the most dense sand (solid) will sink to the bottom.

However, there are some exceptions,
example, water
ice happens to less dense than water but it is a solid, the molecules of water happen to structure themselves in a way that makes them take up more space than water molecules following around each other

No that answer is wrong. you have written the function of mitochondria in chloroplast and function of chloroplast in mitochondria.