MCQ
The correct order of $E^o\, M^{2+}/M$ values with negative sign for the four successive elements $Cr, Mn, Fe$ and $Co$ is
- A$Cr > Mn > Fe > Co$
- ✓$Mn > Cr > Fe > Co$
- C$Cr > Fe > Mn > Co$
- D$Fe > Mn > Cr > Co$
✓
Answer
Correct option: B.
$Mn > Cr > Fe > Co$
b
Usually across the first transition series, the negative values for standard electrode potential decrease except for $Mn$ due to stable $d^5$-configuration.
Usually across the first transition series, the negative values for standard electrode potential decrease except for $Mn$ due to stable $d^5$-configuration.
The electronic configuration of various elements in $Mn ^{2+}$ state is:
$Cr -[\operatorname{Ar}] 3 d ^4$
$Mn - Cr -[ Ar ] 3 d ^5 \quad$-half filled most stable.
$Fe - Cr -[ Ar ] 3 d ^6$
$Co - Cr -[ Ar ] 3 d ^7$
So, based on above facts the correct order is $Mn\, >\, Cr\, > \,Fe \,> \,Co \text {. }$
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