Read the passage carefully and answer the Questions.

In the formation of coordination complexes, if the inner d orbital (n-1d) is used in hybridisation, the complex, is called an inner orbital or low spin or spin paired complex. And if it uses outer d orbital (nd) in hybridisation (like $sp^3d^2$), it is called outer orbital or high spin or spin free complex. The degeneracy of the d orbitals has been removed due to ligand electron-metal electron repulsions in the complex. This splitting of the degenerate levels due to the presence of ligands in a definite geometry is termed as crystal field splitting. For coordination complexes, the magnetic moment is determined by the number of unpaired electrons and is calculated by using the 'spin-only' formula, $μ = \sqrt{n (n+2)}$ where $n$ is the number of unpaired electrons and $μ$ is the magnetic moment in units of Bohr magneton (BM). The coordination compounds are of great importance. These compounds are widely present in the mineral, plant and animal worlds and are known to play many important functions in the area of analytical chemistry, metallurgy, biological systems, industry and medicine.

Fe(II) octahedral complexes can show different 'spin only' magnetic moments for arrangements in the presence of weak and strong ligands. The 'spin only' magnetic moments of these complexes with weak and strong ligands, respectively, are

4.90 BM and 0 BM

The correct answer is Option (2) → 4.90 BM and 0 BM

First determine the electronic configuration of Fe²⁺.

Fe = [Ar] 3d⁶4s²

Fe²⁺ → 3d⁶

In an octahedral field, the splitting of d-orbitals occurs into: t₂g and e_g levels.

Case 1: Weak field ligands (High-spin complex)

Weak ligands such as H₂O, F⁻, Cl⁻ produce small crystal field splitting, so electrons occupy higher orbitals before pairing.

Configuration: t₂g⁴ e_g²

Number of unpaired electrons = 4

Magnetic moment formula: μ = √[n(n + 2)]

μ = √[4(4 + 2)]

μ = √24

μ ≈ 4.90 BM

Case 2: Strong field ligands (Low-spin complex)

Strong ligands such as CN⁻ or CO cause large splitting, leading to pairing of electrons.

Configuration: t₂g⁶ e_g⁰

Number of unpaired electrons = 0

Magnetic moment: μ = 0 BM

Final Result - Weak ligand → 4.90 BM Strong ligand → 0 BM