The $E^{\circ}_{M^{+3}/M^{2+}}$ values for $Cr, \; Mn, \; Fe$ and $Co$ are $-0.41, \; +1.57, \; + 0.77$ and $+1.97 /;\;V$ respectively. For which one of these metals the change in oxidation state form $+2$ and $+3$ is easiest ?

Question

( A ) Cr
( B ) Mn
( C ) Fe
( D ) Co