Which of the following ion configurations has zero $CFSE$ in both strong and weak field ligands in an octahedral complex?

Consider the following complexes:
$[CoCl(NH_3)_5]^{2+},$ $[Co(CN)_6]^{3-}$
$(A)$ $(B)$
$[Co(NH_3)_5(H_2O)]^{3+},$ $[Cu(H_2O)_4]^{2+}$
$(C)$ $(D)$
The correct order of $A, B, C,$ and $D$ in terms of the wavenumber of light absorbed is:

Which of the following has zero Crystal Field Stabilization Energy $(CFSE)$ value in an octahedral field?

Which of the following cannot be explained by crystal field theory?

For a $d^{4}$ metal ion in an octahedral field,the correct electronic configuration is:

The $CFSE$ for $[CoCl_6]^{4-}$ complex is $18000 \ cm^{-1}$. The $\Delta_t$ for $[CoCl_4]^{2-}$ will be ........... $cm^{-1}$.