Which among the following ligands has the highest field strength?

Which ligand among the following has the highest splitting power of $d$-orbitals of the central metal ion?

Using crystal field theory,draw energy level diagrams,write the electronic configuration of the central metal atom/ion,and determine the magnetic moment value for the following:
$(i)$ $[CoF_{6}]^{3-}, [Co(H_{2}O)_{6}]^{2+}, [Co(CN)_{6}]^{3-}$
$(ii)$ $[FeF_{6}]^{3-}, [Fe(H_{2}O)_{6}]^{2+}, [Fe(CN)_{6}]^{4-}$

The crystal field theory is successful in explaining which of the following?
$I.$ Ligands as point charges;
$II.$ Formation and structures of complexes.
$III.$ Colour;
$IV.$ Magnetic properties;
$V.$ Covalent character of metal-ligand bonding.

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

If the crystal field splitting energy of a tetrahedral complex $\Delta_t$ of the type $[ML_4]^{n+}$ is $x \ eV$,what is the crystal field splitting energy with respect to an octahedral complex,$[ML_6]^{n+}$?