The homoleptic and octahedral complex of $Co^{2+}$ and $H_2O$ has $.......$ unpaired electron$(s)$ in the $t_{2g}$ set of orbitals.

Given below are two statements:
Statement $I$: Presence of a large number of unpaired electrons in transition metal atoms results in higher enthalpies of their atomisation.
Statement $II$: $d_{xy} = d_{xz} = d_{yz} < d_{x^2-y^2} = d_{z^2}$ and $d_{x^2-y^2} < d_{xy} = d_{xz} = d_{yz}$ are the $d$-orbital splittings in $[Fe(H_2O)_6]^{3+}$ and $[Ni(Cl)_4]^{2-}$ complex ions respectively.
In the light of the above statements, choose the correct answer from the options given below:

The Crystal Field Stabilization Energy $(CFSE)$ and magnetic moment (spin-only) of an octahedral aqua complex of a metal ion $(M^{2+})$ are $-0.8\, \Delta_{0}$ and $3.87\, BM$,respectively. Identify $(M^{2+})$:

For which of the following pairs of complexes is the crystal field splitting energy $\Delta_0$ for $II > \Delta_0$ for $I$?

$I$	$II$
$(a). [Cr(H_2O)_6]^{2+}$	$[Cr(H_2O)_6]^{3+}$
$(b). [Fe(H_2O)_6]^{3+}$	$[Fe(CN)_6]^{3-}$
$(c). [Fe(CN)_6]^{3-}$	$[Ru(CN)_6]^{3-}$
$(d). [NiF_6]^{4-}$	$[NiF_6]^{2-}$

The crystal field splitting energy of $[Co(oxalate)_3]^{3-}$ complex is '$n$' times that of the $[Cr(oxalate)_3]^{3-}$ complex. Here '$n$' is [Assume $\Delta_0 \gg P$].

Which of the following is the correct order of crystal field splitting strength for ligands based on the donor atom?