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ChemistryNEET 2024Transition elements: trends and properties

The d- and f-Block Elements

The E∘E^\circ value for the Mn3+/Mn2+\mathrm{Mn^{3+}/Mn^{2+}} couple is more positive than that of Cr3+/Cr2+\mathrm{Cr^{3+}/Cr^{2+}} or Fe3+/Fe2+\mathrm{Fe^{3+}/Fe^{2+}} due to the change of:

  1. A.d5d^5 to d2d^2 configuration
  2. B.d4d^4 to d5d^5 configuration✓
  3. C.d3d^3 to d5d^5 configuration
  4. D.d5d^5 to d4d^4 configuration

Solution

Mn3+\mathrm{Mn^{3+}} is d4d^4; gaining an electron gives the stable half-filled d5d^5 configuration of Mn2+\mathrm{Mn^{2+}}. This extra stability makes the reduction unusually favourable, i.e. E∘E^\circ unusually positive.

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