Which one of the following element has the greatest  tendency to convert from +3 $\to$ +2 state in aqueous solution ?

${\mathrm{E}}_{{\mathrm{M}}^{3+}/{\mathrm{M}}^{2+}}^0$values are negative for Ti, V, Cr and positive for Mn, Fe and Co.

${\mathrm{E}}_{{\mathrm{M}}^{3+}/{\mathrm{M}}^{2+}}^0$value is most positive for cobalt  (1.97 V). 

Coblat has the greatest  tendency to convert from +3$\to$+2 state in aqueous solution.