Which of the following intermolecular forces is the weakest?

Dispersion forces, also known as London dispersion forces, are indeed the weakest type of intermolecular force. These forces arise from temporary fluctuations in electron densities within molecules, leading to the formation of instantaneous dipoles. These temporary dipoles can induce dipoles in neighboring molecules, creating a very weak attractive force between them.

While they can be significant in large molecules or in aggregates of nonpolar substances, dispersion forces are generally much weaker than other types of intermolecular forces. For example, hydrogen bonding is much stronger due to the significant polarity and the presence of highly electronegative atoms like nitrogen, oxygen, or fluorine bonded to hydrogen. Similarly, dipole-dipole interactions occur between polar molecules and involve permanent dipoles, making them stronger than dispersion forces. Ion-dipole interactions are even stronger, as they involve the attraction between charged ions and polar molecules.

Thus, dispersion forces, while important in various contexts (especially in nonpolar substances), are the weakest form of intermolecular attractive forces among the options presented.