Question

Which of the following compound is paramagnetic in nature?

• A. \([ \text{Ni(CO)}_4 ] \)
• B. \([ \text{Ni(CN)}_4 ]^{2-} \)
• C. \([ \text{NiCl}_4 ]^{2-} \)
• D. \([ \text{Co(H}_2\text{O)}_6 ]^{3+} \)

Hint:

In transition metal complexes, the presence of unpaired electrons in the d-orbitals causes paramagnetism.

Answer 1

The Correct Option is C

For \(\text{Ni(CO)}_4\): \[ \text{Ni}^{2+} : 3d^8 4s^2 \quad \text{paramagnetic because of unpaired electrons} \] For \(\text{Ni(CN)}_4^{2-}\): \[ \text{Ni}^{2+} : 3d^8 4s^2 \quad \text{CN}^- \text{ is SFL} \quad \text{paramagnetic} \] For \(\text{NiCl}_4^{2-}\): \[ \text{Ni}^{2+} : 3d^8 \quad \text{paramagnetic} \] For \([ \text{Co(H}_2\text{O)}_6 ]^{3+}\): \[ \text{Co}^{3+} : 3d^6 \quad \text{dsp}^3 \quad \text{no unpaired electrons, diamagnetic} \] Step 2: Conclusion.
The correct answer is (3) \([ \text{NiCl}_4 ]^{2-}\) since it is paramagnetic.