Question

The E° value for the Mn3+/Mn2+ couple is more positive than that of Cr3+/Cr2+ or Fe3+/Fe2+ due to change of

• A. d5 to d4 configuration
• B. d5 to d2 configuration
• C. d4 to d5 configuration
• D. d3 to d5 configuration

Answer 1

Answer: (C)

d4 to d5 configuration

Answer 2

1. $Mn^{3+}$ has a $d^4$ configuration, which upon reduction to $Mn^{2+}$ becomes $d^5$, a half-filled stable configuration.
2. This stability contributes to the more positive $E^o$ value for $Mn^{3+}/Mn^{2+}$ compared to Cr or Fe.