A transition metal (M) among Mn, Cr, Co and Fe has the highest standard electrode potential $\left( {{M^{3 + }}/{M^{2 + }}} \right)$. It forms a metal complex of the type ${\left[ {M{{(CN)}_6}} \right]^{4 - }}$. The number of electrons present in the ${e_g}$ orbital of the complex is ____
