Regarding Periodic Table and Atoms: Which one has more density – solid, liquid or gas

Gases are always the least dense phase.

With solids and liquids, however, it depends on the substance.

Water, for example, has a liquid phase which is more dense than its solid phase (which is why ice cubes float).

Nitrogen, however, has a solid phase which is more dense than its liquid phase (solid nitrogen sinks in liquid nitrogen).