Final answer:
NF3 is the substance that experiences dipole-dipole forces due to its polar nature, causing an unequal distribution of electrons and resulting in a molecular dipole.
Step-by-step explanation:
The substance among the given options that experiences dipole-dipole forces is NF3 (Nitrogen trifluoride). These forces occur because NF3 is a polar molecule, which means it has a net unequal distribution of electrons. This results in a partial positive charge on the nitrogen atom and partial negative charges on the fluorine atoms, creating a separation of charge known as a dipole. The electrostatic attractions between the oppositely charged ends of these polar molecules signify the presence of dipole-dipole interactions. In contrast, molecules like BF3, CS2, and CCl4 are nonpolar and do not exhibit dipole-dipole attractions, primarily experiencing London dispersion forces or van der Waals forces.