Q32 / 180 · AIIMS 2013 · Chemistry

Assertion : Bond lengths of $\mathrm{P}-\mathrm{Cl}$ bonds in gaseous $\mathrm{PCl}_5$ and solid $\mathrm{PCl}_5$ are not equal. Reason : Because in solid state two $\mathrm{PCl}_5$ molecules are associated.

  • Correct answer
    A
    If both assertion and reason are true and reason is the correct explanation of assertion.
  • B
    If both assertion and reason are true but reason is not the correct explanation of assertion.
  • C
    If assertion is true but reason is false.
  • D
    If both assertion and reason are false.

Solution

As in solid state, $\mathrm{PCl}_5$ exists as an ionic solid $\left[\mathrm{PCl}_4\right]^{+}\left[\mathrm{PCl}_6\right]^{-}$in which the cation, $\left[\mathrm{PCl}_4\right]^{+}$ is tetrahedral and the anion, $\left[\mathrm{PCl}_6\right]^{-}$is octahedral. $\mathrm{PCl}_5$ in gaseous state has trigonal bipyramidal structure in which three equatorial bonds are equivalent, while the two axial bonds are longer than equatorial bonds due to more bond pair repulsion.

Hence, the correct answer is option: 'A'.

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