Question

Total number of unpaired electrons in the complex ion [Co(NH$_3$)$_6$]$^{3+}$ and [NiCl$_4$]$^{2-}$ is

Answer 1

Correct Answer: 2

[Co(NH$_3$)$_6$]$^{3+}$
-Oxidation state of Co: $+3$
-Electronic configuration of Co$^{3+}$: $3d^6$
-NH$_3$ is a strong field ligand, causing pairing of electrons in the $t_{2g}$ orbitals.
-Distribution: $t_{2g}^6 e_g^0$ 
-Unpaired electrons: 0
[NiCl$_4$]$^{2-}$
-Oxidation state of Ni: $+2$
-Electronic configuration of Ni$^{2+}$: $3d^8$
-Cl$^-$ is a weak field ligand, causing no pairing of electrons.
-Distribution: $e_g^2 t_{2g}^6$
-Unpaired electrons: 2
Total unpaired electrons: $0 + 2 = 2$