Question

how do molecules in a solid differ from those in a liquid or gas

Answer 1

Molecules are similar, strength of forces between molecules
Are stronger in solid

Answer 2

molecules in solids r very tightly packed the intermolecular distance between them is very very less. because of the highly effective wanderwalls forces. while the molecules in liquid or gases r loosely packed. and therefore the intermolecular distance is more because the less effective wanderwalls forces.

Answer 3

van der Waals' forces in solids aren't any stronger than they are in liquids or gases - the point is that other things, like molecular bonding, are present. van der Waals' forces are fleeting attractions between atoms or molecules due to statistical fluctuations in electron density and polarization, while molecular bonds are much more powerful and permanent and lock the molecules into place.