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  4. The EM3 + / M2 +o values for Cr, Mn, Fe and Co are -0.41, +1.57, +0.77 and +1.97 V respectively. For which one of following metal the change in oxidation state from +2 to +3 easiest?

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Q. The $E_{M^{3 +} / M^{2 +}}^{o}$ values for Cr, Mn, Fe and Co are -0.41, +1.57, +0.77 and +1.97 V respectively. For which one of following metal the change in oxidation state from +2 to +3 easiest?

NTA AbhyasNTA Abhyas 2022

Solution:

Here $E_{R P}^{o}$ of Cr = - 0.41 so its $E_{O P}^{o}$ is 0.41.
As here $E_{O P}^{o}$ for $Cr^{2 +}/Cr^{3 +}$ is maximum +0.41 V so $Cr^{2 +}$ will be easily oxidised to $Cr^{3 +}$ .
For rest of the metals $E_{O P}^{o}$ will be negative so they have less tendency to be oxidized then Cr here.