Question

Halogens in un combined state exist as diatomic molecules ,but they these discrete molecules have vander waal forces, why?

Answer 1

Well, basically because these molecules have electrons...

Explanation:

And electronic clouds are polarizable....and in the absence of other intermolecular forces, the intermolecular interaction on the basis of the polarizability of the electron cloud can be significant.

And the halogen series displays ALL the states of matter. Difluorine and dichlorine are room temperature gases. Dibromine is one of the few elemental liquids (and the element is treated with a great deal of respect given its corrosiveness). And diiodine is a sublimable solid.... As the electronic cloud gets bigger as we go down the Group, `"van der Waals"` forces become more significant, and the elemental states reflect this.