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?

Step-by-step 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 C r 2 + / C r 3 + is maximum +0.41 V so C r 2 + will be easily oxidised to C r 3 + . For rest of the metals E O P o will be negative so they have less tendency to be oxidized then Cr here.