Here's why:
* Solids have a fixed shape and volume because their molecules are tightly packed in a regular, repeating arrangement called a crystal lattice. This close proximity and strong attraction between molecules make solids rigid and incompressible.
* Liquids have a fixed volume but take the shape of their container. The molecules are closer together than in a gas, but they have more freedom to move around than in a solid.
* Gases have no fixed shape or volume. Their molecules are far apart and move freely, colliding with each other and the walls of their container.
So, while liquids have molecules closer together than gases, solids have the closest packing and strongest intermolecular forces.
