This is the weakest intermolecular force. It forms when all of the electrons randomly swarm to one side of a molecule, creating an instantaneous dipole.

London dispersion force

Explanation:

London dispersion force (Instantaneous dipole-induced dipole interaction) is the weakest intermolecular force. It can occur in atoms or molecules (e.g. Helium atom) which have no permanent dipole, instantaneous dipoles will arise as a result of a momentary imbalance in electron distribution. This interaction only lasts for a very short time (i.e. a fraction of a microsecond).

it is the most commonly accepted one