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

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

ChemistryNEET 2024Transition elements: trends and properties

The d- and f-Block Elements

The $E^{\circ}$ value for the $M n^{3 +} /M n^{2 +}$ couple is more positive than that of $C r^{3 +} /C r^{2 +}$ or $F e^{3 +} /F e^{2 +}$ due to the change of:

A. $d^{5}$ to $d^{2}$ configuration
B. $d^{4}$ to $d^{5}$ configuration✓
C. $d^{3}$ to $d^{5}$ configuration
D. $d^{5}$ to $d^{4}$ configuration

Solution

$M n^{3 +}$ is $d^{4}$ ; gaining an electron gives the stable half-filled $d^{5}$ configuration of $M n^{2 +}$ . This extra stability makes the reduction unusually favourable, i.e. $E^{\circ}$ unusually positive.

Save for spaced revision (free account)

The d- and f-Block Elements

More from this chapter in past papers