Discuss the nature of bonding in the following coordination entities on the basis of valence bond theory:
$(i)$ $[Fe(CN)_6]^{4-}$
$(ii)$ $[FeF_6]^{3-}$
$(iii)$ $[Co(C_2O_4)_3]^{3-}$
$(iv)$ $[CoF_6]^{3-}$

(N/A) $(i)$ $[Fe(CN)_6]^{4-}$: Iron is in $+2$ oxidation state $(Fe^{2+}: 3d^6)$. $CN^-$ is a strong field ligand,causing pairing of $3d$ electrons. It undergoes $d^2sp^3$ hybridization. The complex is octahedral and diamagnetic.
$(ii)$ $[FeF_6]^{3-}$: Iron is in $+3$ oxidation state $(Fe^{3+}: 3d^5)$. $F^-$ is a weak field ligand,so no pairing occurs. It undergoes $sp^3d^2$ hybridization. The complex is octahedral and paramagnetic.
$(iii)$ $[Co(C_2O_4)_3]^{3-}$: Cobalt is in $+3$ oxidation state $(Co^{3+}: 3d^6)$. Oxalate $(C_2O_4^{2-})$ is a bidentate ligand. Although it is often considered a weak field ligand,in this specific complex,it forms a low-spin octahedral complex with $d^2sp^3$ hybridization. The complex is octahedral and diamagnetic.
$(iv)$ $[CoF_6]^{3-}$: Cobalt is in $+3$ oxidation state $(Co^{3+}: 3d^6)$. $F^-$ is a weak field ligand,so no pairing occurs. It undergoes $sp^3d^2$ hybridization. The complex is octahedral and paramagnetic.