Read the passage carefully and answer.

The crystal field theory (CFT) is an electrostatic model which considers the metal-ligand bond to be ionic arising purely from electrostatic interactions between the metal ion and the ligand. Ligands are treated as point charges in case of anions or dipoles in case of neutral molecules. The five d orbitals in an isolated gaseous metal atom/ion have same energy, i.e., they are degenerate. This degeneracy is maintained if a spherically symmetrical field of negative charges surrounds the metal atom/ion. However, when this negative field is due to ligands (either anions or the negative ends of dipolar molecules like $NH_3$ and $H_2O$) in a complex, it becomes asymmetrical and the degeneracy of the d orbitals is lifted. It results in splitting of the d orbitals. The pattern of splitting depends upon the nature of the crystal field.

The hybridisation and magnetism of the complexes $[Co(C_2O_4)_3]^{3-}$ and $[Mn(CN)_6]^{3-}$ respectively is

($d^2sp^3$, diamagnetic) and ($d^2sp^3$, paramagnetic)

The correct answer is Option (3) → ($d^2sp^3$, diamagnetic) and ($d^2sp^3$, paramagnetic)

The correct answer is Option (C) →
(d²sp³, diamagnetic) and (d²sp³, paramagnetic)

1. Complex: [Co(C₂O₄)₃]³⁻
In [Co(C₂O₄)₃]³⁻, cobalt is in +3 oxidation state (3d⁶). Oxalate (C₂O₄²⁻) acts as a strong field ligand, causing pairing of electrons. Hence, the complex shows d²sp³ hybridisation and is diamagnetic.

Reasoning:

• Oxidation state:
  x + 3(−2) = −3 → x = +3

• Co³⁺ → 3d⁶

• Strong field ligand → electrons pair in t₂g

• Electronic configuration: t₂g⁶ e_g⁰ (no unpaired electrons)

• Inner orbital complex formed → d²sp³

• No unpaired electrons → diamagnetic

• 2. Complex: [Mn(CN)₆]³⁻

  In [Mn(CN)₆]³⁻, manganese is in +3 oxidation state (3d⁴). Cyanide (CN⁻) is a strong field ligand, but in d⁴ configuration, pairing still leaves unpaired electrons. Hence, the complex shows d²sp³ hybridisation and is paramagnetic.

Reasoning:

• Oxidation state:
  x + 6(−1) = −3 → x = +3

• Mn³⁺ → 3d⁴

• Strong field ligand → low spin arrangement

• Electronic configuration: t₂g⁴ e_g⁰

• 2 unpaired electrons remain

• Inner orbital complex → d²sp³

• Presence of unpaired electrons → paramagnetic

• Final Conclusion

[Co(C₂O₄)₃]³⁻ → d²sp³, diamagnetic
[Mn(CN)₆]³⁻ → d²sp³, paramagnetic