The correct order of the calculated spin - only magnetic moments of complexes (A) to (D) is :
(A) `Ni(CO)_(4)`
(B) `[Ni(H_(2)O)_(6)]Cl_(2)`
(C) `Na_(2)[Ni(CN)_(4)]`
(D) `PdCl_(2)(PPh_(3))_(2)`

Options

A. `(A)~~ (C) lt (B) ~~(D)`
B. `(C)~~ (D) lt (B) lt (A)`
C. `(C)lt (D) lt (B) lt(A)`
D. `(A)~~ (C) ~~ (D) lt(B)`

Answer

To determine the correct order of the calculated spin-only magnetic moments of the complexes (A) to (D), we need to analyze each complex based on the number of unpaired electrons present in their electronic configurations.

### Step-by-Step Solution:

1. **Analyze Complex (A): `Ni(CO)4`**
- **Oxidation State**: Ni is in the 0 oxidation state.
- **Electronic Configuration**: Ni (atomic number 28) has the configuration [Ar] 3d^8 4s^2.
- **Ligand Strength**: CO is a strong field ligand, which causes pairing of electrons.
- **Unpaired Electrons**: All electrons will pair up, resulting in 0 unpaired electrons.
- **Magnetic Moment**: 0 (since there are no unpaired electrons).

2. **Analyze Complex (B): `[Ni(H2O)6]Cl2`**
- **Oxidation State**: Ni is in the +2 oxidation state.
- **Electronic Configuration**: Ni^2+ has the configuration 3d^8.
- **Ligand Strength**: H2O is a weak field ligand, which leads to some unpaired electrons.
- **Unpaired Electrons**: In an octahedral field, the 3d electrons fill as follows: T2g (6 electrons) and Eg (2 electrons). The last two electrons will remain unpaired.
- **Magnetic Moment**: There are 2 unpaired electrons.
- Calculation: \( \mu = \sqrt{n(n + 2)} = \sqrt{2(2 + 2)} = \sqrt{8} = 2.83 \, \mu_B \).

3. **Analyze Complex (C): `Na2[Ni(CN)4]`**
- **Oxidation State**: Ni is in the +2 oxidation state.
- **Electronic Configuration**: Ni^2+ has the configuration 3d^8.
- **Ligand Strength**: CN^- is a strong field ligand, which causes pairing of electrons.
- **Unpaired Electrons**: All electrons will pair up, resulting in 0 unpaired electrons.
- **Magnetic Moment**: 0 (since there are no unpaired electrons).

4. **Analyze Complex (D): `PdCl2(PPh3)2`**
- **Oxidation State**: Pd is in the +2 oxidation state.
- **Electronic Configuration**: Pd (atomic number 46) has the configuration [Kr] 4d^10.
- **Ligand Strength**: Cl^- is a weak field ligand, and PPh3 is a neutral ligand.
- **Unpaired Electrons**: In this case, Pd^2+ has a filled d-orbital (4d^8) and will have no unpaired electrons due to pairing.
- **Magnetic Moment**: 0 (since there are no unpaired electrons).

### Summary of Magnetic Moments:
- Complex (A): 0
- Complex (B): 2.83
- Complex (C): 0
- Complex (D): 0

### Correct Order of Magnetic Moments:
The correct order of the calculated spin-only magnetic moments of the complexes (A) to (D) is:
**(B) > (A) = (C) = (D)**