The correct order of E0M2+∣M values with negative sign for the four successive elements Cr, Mn, Fe and Co is

A
$Cr > Mn > Fe > Co$
B
$Mn > Cr > Fe > Co$
C
$Cr > Fe > Mn > Co$
D
$Fe > Mn > Cr > Co$

Solution:

The $E^{\circ}$ values are as follows.

$E^{\circ} ({Cr}^{2 +} ∣ Cr) = - 0.91 V; E^{\circ} ({Mn}^{2 +} ∣ Mn) = 1.18 V; E^{\circ} ({Fe}^{2 +} ∣ Fe) = - 0.44 V; E^{\circ} ({Co}^{2 +} ∣ Co) = - 0.28 V$

Electrode potential becomes less negative as one goes from left to right across 3d transition elements. Chromium seems to be exceptional case since its (first+ second) ionization energy is larger than that of manganese. In general, larger the (first+ second) ionization energy, lesser negative is the electrode potential.

The correct order of $E^{0} M^{2 +} ∣ M$ values with negative sign for the four successive elements $Cr, Mn, Fe$ and $Co$ is

Solution:

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