According to crystal field theory, for which of the following coordination entities is $\Delta_o$ maximum?

In which of the following complexes of the $Co$ (at. no. $27$),will the magnitude of $\Delta_o$ be the highest?

The correct order of energies of $d-$ orbitals of a metal ion in a square planar complex is:

The wavelengths of light absorbed by the complexes $[Ni(H_2O)_6]^{2+}$,$[Ni(en)_3]^{2+}$,and $[Ni(H_2O)_4en]^{2+}$ are $\lambda_1$,$\lambda_2$,and $\lambda_3$ respectively. The correct order of wavelengths is:

In which one of the following complexes does the metal ion have a $t_{2g}^3 e_g^2$ configuration?

Identify the complex ion with electronic configuration $t_{2g}^3 e_g^2$.