Which complex shows the highest crystal field stabilisation energy?

For which of the following types of ions is the number of unpaired electrons in octahedral complexes fixed at the same number as in the free ion,no matter how weak or strong the crystal field is?

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

What is the correct electronic configuration of the central atom in $K_{4}[Fe(CN)_{6}]$ based on crystal field theory?

Match List-$I$ with List-$II$.
List-$I$ (Chromium $(III)$ Complexes) - List-$II$ ($\Delta_o$ $(cm^{-1})$)
$A$. $[Cr(CN)_6]^{3-}$ - $I$. $15,060$
$B$. $[CrF_6]^{3-}$ - $II$. $17,400$
$C$. $[Cr(H_2O)_6]^{3+}$ - $III$. $22,300$
$D$. $[Cr(en)_3]^{3+}$ - $IV$. $26,600$
Choose the correct answer from the options given below:

Crystal field stabilization energy for complex $[Co(CN)_6]^{3-}$ will be