In which state of matter are intermolecular forces strongest?
Solids have the strongest intramolecular forces.
I think you meant intramolecular forces, because intermolecular forces are the forces within the molecule while intramolecular forces are the forces between atoms that makes up the molecule.
I am going to assume you mean the 3 big states: solids, liquids and gases.
Atomic attraction varies on multiple things but they all come back to the kinetic energy of the particles.
When particles are moving slowly, this is due to their low kinetic energy, which ultimately makes the attraction larger. As the temperature continues to drop, the matter forms a solid.
Due to the solid's low kinetic energy, particles have no "time" to move around, the particles have more "time" to be attracted.
Therefore, solids have the strongest intramolecular forces (because they have the strongest attraction).
Hope this helps :)
P.S. Inter- = Van der Waal