Concept:The weakest force between separate molecules is an intermolecular attraction, not a strong intramolecular bond.Explanation:Ionic, covalent, and co-ordinate covalent forces hold atoms within a molecule together. These are strong intramolecular bonds. Van der Waals forces act between different molecules and are much weaker than any bond inside a molecule. Therefore, the weakest attractive force between two molecules is van der Waals.Answer:D. van der Waals