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
What happens to the population density and competition if the birth rate decreases? The birth rate would increase is the population density competition increased. Hope I helped.
