Vander waal forces are defined as the weak electric forces which tend to attract the neutral molecules towards each other in gases, liquefied and solidified gases. And, it is also present in all organic liquids and solids.
Vander wall forces are basically present in all type of molecules. More is the number of carbon atoms present in a molecule more will be the presence of Vander waal forces.
As a result, butanol will have strongest intermolecular force of attraction because it contains more number of carbon atoms and also it has more electronegative oxygen atom.
Whereas n-pentane will have the weakest intermolecular force of attraction between its atoms.
