Question 5

Analyzing the statements: (A) The potential energy between two point charges is proportional to $1/r$, while for a point dipole and a point charge, it is proportional to $1/r^2$. Since $1/r^2$ approaches zero faster than $1/r$ as $r \to \infty$, the statement is incorrect. (B) For rotating polar molecules (Keesom interaction), the average potential energy is proportional to $1/r^6$, not $1/r^3$. $1/r^3$ dependence is for static dipoles. Thus, the statement is incorrect. (C) Dipole-induced dipole interaction (Debye force) energy is proportional to $1/r^6$ and depends on the polarizability of the non-polar molecule and the dipole moment of the polar molecule; it is independent of temperature. Thus, the statement is correct. (D) Nonpolar molecules attract each other via London dispersion forces (induced dipole-induced dipole interactions). Thus, the statement is correct.