JEE Main · 2021 · Shift-IIeasyBOND-146

The interaction energy of London forces between two particles is proportional to rx, where r is the distance between…

Chemical Bonding · Class 11 · JEE Main Previous Year Question

Question

The interaction energy of London forces between two particles is proportional to rxr^x, where r is the distance between the particles. The value of x is:

Options
  1. a

    6

  2. b

    -6

  3. c

    3

  4. d

    -3

Correct Answerb

-6

Detailed Solution

🧠 London (dispersion) forces arise from instantaneous dipole–induced dipole interactions. Their interaction energy has a specific distance dependence.

🗺️ London force interaction energy:

ELondon1r6E_{\text{London}} \propto \frac{1}{r^6}

This can be written as rxr^x where x=6x = -6.

⚡ Distance dependence summary:

| Interaction | Energy ∝ | |------------|---------| | Ion–ion | 1/r1/r | | Ion–dipole | 1/r21/r^2 | | Dipole–dipole (fixed) | 1/r31/r^3 | | London dispersion | 1/r61/r^6 |

The very steep r6r^{-6} dependence means London forces become negligible quickly as distance increases — they are significant only at very short (contact) distances.

Answer: x=6\boxed{\text{Answer: } x = -6}

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