JEE Advanced 2025 Paper 2 Q05 Chemistry Physical Chemistry Solutions & Colligative Properties Medium

JEE Advanced 2025 Paper 2 · Q05 · Solutions & Colligative Properties

The correct statement(s) about intermolecular forces is(are):

  1. A. The potential energy between two point charges approaches zero more rapidly than the potential energy between a point dipole and a point charge as the distance between them approaches infinity.
  2. B. The average potential energy of two rotating polar molecules that are separated by a distance $r$ has $1/r^3$ dependence.
  3. C. The dipole-induced dipole average interaction energy is independent of temperature.
  4. D. Nonpolar molecules attract one another even though neither has a permanent dipole moment.
JEE Advanced multi-correct — pick every correct option, then check.
Reveal answer + step-by-step solution

Correct answer:C, D

Solution

(A) $U_{q-q} \sim 1/r$ and $U_{dipole-q} \sim 1/r^2$; so dipole-charge falls off faster than charge-charge. The statement is reversed. FALSE. (B) Keesom interaction (rotating polar molecules) averages over orientations to give $U \sim 1/r^6$, NOT $1/r^3$. FALSE. (C) Debye (dipole-induced dipole) interaction depends on polarizability and dipole moment; the average is independent of temperature (induced dipole follows the inducing dipole instantaneously). TRUE. (D) London dispersion forces arise from instantaneous-dipole/induced-dipole interactions and act between any pair of atoms/molecules, including non-polar ones. TRUE. Correct: (C), (D).

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