\(E_{M n^{2}+/ M n}^{\circ}=-1.18 V\)
\(E_{C r^{2}+/ C r}^{\circ}=-0.9 V\)
\(E_{F e^{2+} / F e}^{\circ}=-0.44 V\) and
\(E_{C o^{2}+/ C o}^{\circ}=-0.28 V\)
The correct order of \(E_{M^{2+} / M}^{\circ}\) values without
considering negative sign would be
\(M n^{2+}>C r^{2+}>F e^{2+}>C o^{2+}\)
$(1$ ફેરાડે $= 96500\, C,$ પરમાણ્વીય દળ of $Co = 59)$