The value of $$E_{{M^{2 + }}/M}^ \circ $$ for given metal ions are

$$E_{M{n^{2 + }}/Mn}^ \circ = - 1.18\,V,\,\,$$

$$E_{C{r^{2 + }}/Cr}^ \circ = - 0.9V,$$

$$E_{F{e^{2 + }}/Fe}^ \circ = - 0.44\,V$$ and

$$E_{C{o^{2 + }}/Co}^ \circ = - 0.28\,V.$$

So when we consider these values with a negative sign (i.e., taking the magnitude of the negative potentials), we get the values as :

• $Cr$ : 0.91 V
• $Mn$ : 1.18 V
• $Fe$ : 0.44 V
• $Co$ : 0.28 V

Therefore, the correct order of $E_{M^{2+}/M}^\circ$ values with the negative sign will be :

Mn > Cr > Fe > Co

This matches with option A.