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Question: Answered & Verified by Expert
The purple colour of $\mathrm{KMnO}_{4}$ is due to the transition
Chemistryd and f Block ElementsVITEEEVITEEE 2007
Options:
  • A C.T. $(\mathrm{L} \rightarrow \mathrm{M})$
  • B C.T. $(\mathrm{M} \rightarrow \mathrm{L})$
  • C $\mathrm{d}-\mathrm{d}$
  • D $\mathrm{p}-\mathrm{d}$
Solution:
1525 Upvotes Verified Answer
The correct answer is: C.T. $(\mathrm{L} \rightarrow \mathrm{M})$
The permanganate ion has an intense purple colour. Mn (+ VII) has a d $^{0}$ configuration. So the colour arises from charge transfer and not from d-d spectra. In $\mathrm{MnO}_{4}{ }^{-}$an electron is momentarily changing $\mathrm{O}^{-}$- to $\mathrm{O}^{-}$and reducing the oxidation state of the metal from $\mathrm{Mn}(\mathrm{VII})$ to Mn (VI). Charge transfer requires that the energy levels on the two different atoms are fairly close.
$\mathrm{O}=(8)=2,6$
$\quad\quad\quad\quad$ K L
$\mathrm{Mn}(25)=2,8,15$
$\quad\quad\quad\quad$ K L M
hence the charge transfer occurs from $\mathrm{L} \rightarrow \mathrm{M}$

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