Which one of the following complexes has the highest magnitude of crystal field splitting energy $\left(\Delta_0\right)$?

$A$ 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 $.........$

The spin magnetic moment of an octahedral complex having $CFSE = -0.8 \Delta_{0}$ and surrounded by weak field ligands can be:

Which of the following comparisons is correct for the crystal field splitting energy $\Delta_0$ of the following complexes?
$I$- $[Co(H_2O)_6]^{2+}$
$II$- $[Co(H_2O)_6]^{3+}$
$III$- $[Fe(H_2O)_6]^{3+}$
$IV$- $[Fe(CN)_6]^{3+}$

The energies of $d_{xy}$ and $d_{z^2}$-orbitals in octahedral and tetrahedral transition metal complexes are such that

The complex ion that will lose its crystal field stabilization energy upon oxidation of its metal to $+3$ state is