Calculate the crystal field stabilization energy $(CFSE)$ in $[Co(CN)_6]^{3-}$.

The degeneracy of $d-$orbitals is lost under:
$I$. Strong field ligand
$II$. Weak field ligand
$III$. Mixed field ligand
$IV$. Chelated ligand field
Choose the correct code:

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

Match List-$I$ with List-$II$. Choose the correct answer from the options given below:
| List-$I$ (Complex ion) | List-$II$ (Electronic Configuration) |
| :--- | :--- |
| $A. [Cr(H_2O)_6]^{3+}$ | $I. t_{2g}^2 e_g^0$ |
| $B. [Fe(H_2O)_6]^{3+}$ | $II. t_{2g}^3 e_g^0$ |
| $C. [Ni(H_2O)_6]^{2+}$ | $III. t_{2g}^3 e_g^2$ |
| $D. [V(H_2O)_6]^{3+}$ | $IV. t_{2g}^6 e_g^2$ |

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

The correct increasing order for the wavelengths of absorption in the visible region for the complexes of $Co^{3+}$ is: