Final answer:
The dominant intermolecular force in a mixture of NH3 and KCl is hydrogen bonding among the NH3 molecules. KCl can also interact with NH3 through ion-dipole interactions, but these are secondary to the hydrogen bonding.
Step-by-step explanation:
The dominant intermolecular force (IMF) in a mixture of NH3 (ammonia) and KCl (potassium chloride) would be hydrogen bonding among the NH3 molecules. NH3, being a polar molecule with a significant difference in electronegativity between the nitrogen and hydrogen atoms, has the capability of forming hydrogen bonds, which are strong intermolecular forces. KCl, on the other hand, is an ionic compound that will dissociate in water to form potassium and chloride ions, but when considering the intermolecular forces between NH3 molecules and KCl, it's the hydrogen bonding in NH3 that is the most significant force.
In a mixture, KCl would not actively participate in hydrogen bonding, but it can interact with NH3 through ion-dipole interactions, which are also significant but secondary to hydrogen bonding when discussing the dominant forces in the mixture. Thus, the hydrogen bonds among NH3 molecules remain the primary IMF in the mixture.