Concept: Intermolecular Forces

Intermolecular forces are attractive forces that exist between molecules. These forces include ion-dipole, dipole-dipole, hydrogen bonding, ion-induced dipole, dipole-induced dipole, and London dispersion forces.

Why (C) is correct:

An ion-induced dipole interaction occurs between an ion and a nonpolar molecule. The electric field of the ion distorts the electron cloud of the nonpolar molecule, inducing a temporary dipole in it. This induced dipole then interacts with the ion.

• In option (C), ${\mathrm{Na}}^{+}$ is an ion, and ${\mathrm{Br}}_2$ is a nonpolar molecule (due to identical atoms and symmetrical structure). The ${\mathrm{Na}}^{+}$ ion will induce a temporary dipole in the ${\mathrm{Br}}_2$ molecule, leading to an ion-induced dipole interaction.

Option Analysis:

• A) ${\mathrm{Li}}^{+}$ and ${\mathrm{H}}_2\mathrm{O}$: ${\mathrm{Li}}^{+}$ is an ion and ${\mathrm{H}}_2\mathrm{O}$ is a polar molecule (due to its bent structure and electronegativity difference between O and H). This interaction is an ion-dipole interaction.
• B) ${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{H}}_2\mathrm{O}$: Both are polar molecules. The primary interaction here is hydrogen bonding, which is a special type of strong dipole-dipole interaction.
• D) ${\mathrm{Br}}_2$ and ${\mathrm{H}}_2\mathrm{O}$: ${\mathrm{Br}}_2$ is a nonpolar molecule, and ${\mathrm{H}}_2\mathrm{O}$ is a polar molecule. This interaction is a dipole-induced dipole interaction.

Correct Answer: (C)