Final answer:
The intermolecular force that predominates between NH3 molecules is hydrogen bonding, which is stronger than the London dispersion forces and dipole-dipole interactions that also exist between ammonia molecules.
Step-by-step explanation:
Among the types of intermolecular forces present in NH3 (ammonia), hydrogen bonding is the predominant force. Ammonia molecules have a nitrogen atom (N) that is significantly more electronegative than the hydrogen atoms (H) it is bonded to. This creates a polar covalent bond within the molecule, resulting in a dipole where the nitrogen has a partial negative charge, and the hydrogens have a partial positive charge.
The hydrogen atoms of one ammonia molecule can form a hydrogen bond with the lone pair electrons of the nitrogen on another ammonia molecule. This interaction is much stronger than London dispersion forces and is responsible for the higher boiling point of NH3 compared to similarly sized molecules without hydrogen bonding. While London dispersion forces and dipole-dipole interactions are also present, they are significantly weaker than the hydrogen bonds in ammonia.