Here's why:

* LDFs are temporary, weak attractions that arise from the instantaneous fluctuations in electron distribution within molecules. They are present in all molecules, but are the only force present in nonpolar molecules.

* Dipole-Dipole forces are stronger than LDFs because they involve permanent dipoles in polar molecules, leading to a more consistent attraction.

* Hydrogen bonds are the strongest type of intermolecular force, occurring when a hydrogen atom is bonded to a highly electronegative atom like oxygen, nitrogen, or fluorine. This creates a very strong dipole and attraction between molecules.

In summary, the strength of intermolecular forces generally increases in this order:

London Dispersion Forces < Dipole-Dipole Forces < Hydrogen Bonds