Same number of unpaired electron is observed in which of the following complexes
(a) `[MnCl_(6)]^(3-)` (b) `[Fe(CN)_(6)]^(3-)`
( c) `[CoF_(6)]^(3-)` (d) `[Ni(NH_(3))_(6)]^(2+)`

Options

A. a and b
B. a & c
C. b & d
D. c & d

Answer

To determine which of the given complexes have the same number of unpaired electrons, we need to analyze the electronic configurations of the metal ions in each complex and consider the effect of the ligands on electron pairing.

### Step-by-Step Solution:

1. **Identify the oxidation states and electronic configurations of the metal ions:**
- (a) **[MnCl6]^(3-)**: Manganese (Mn) has an atomic number of 25. In the +3 oxidation state, its electronic configuration is:
- Mn: 4s² 3d⁵ → Mn³⁺: 3d⁴
- (b) **[Fe(CN)6]^(3-)**: Iron (Fe) has an atomic number of 26. In the +3 oxidation state, its electronic configuration is:
- Fe: 4s² 3d⁶ → Fe³⁺: 3d⁵
- (c) **[CoF6]^(3-)**: Cobalt (Co) has an atomic number of 27. In the +3 oxidation state, its electronic configuration is:
- Co: 4s² 3d⁷ → Co³⁺: 3d⁶
- (d) **[Ni(NH3)6]^(2+)**: Nickel (Ni) has an atomic number of 28. In the +2 oxidation state, its electronic configuration is:
- Ni: 4s² 3d⁸ → Ni²⁺: 3d⁸

2. **Determine the ligand field strength:**
- **Cl⁻** is a weak field ligand, which means it does not cause significant pairing of electrons.
- **CN⁻** is a strong field ligand, which causes pairing of electrons.
- **F⁻** is a weak field ligand, similar to Cl⁻.
- **NH₃** is a moderate field ligand, which can also cause some pairing but not as strongly as CN⁻.

3. **Electron configuration and unpaired electrons:**
- (a) **[MnCl6]^(3-)**:
- 3d⁴ configuration with no pairing:
- Unpaired electrons = 4
- (b) **[Fe(CN)6]^(3-)**:
- 3d⁵ configuration with pairing due to strong field ligand:
- Unpaired electrons = 1
- (c) **[CoF6]^(3-)**:
- 3d⁶ configuration with no pairing:
- Unpaired electrons = 4
- (d) **[Ni(NH3)6]^(2+)**:
- 3d⁸ configuration with some pairing:
- Unpaired electrons = 2

4. **Conclusion:**
- From the analysis, we find:
- [MnCl6]^(3-) has 4 unpaired electrons.
- [CoF6]^(3-) has 4 unpaired electrons.
- [Fe(CN)6]^(3-) has 1 unpaired electron.
- [Ni(NH3)6]^(2+) has 2 unpaired electrons.
- The complexes with the same number of unpaired electrons are **(a) [MnCl6]^(3-)** and **(c) [CoF6]^(3-)**.

### Final Answer:
The complexes with the same number of unpaired electrons are **(a) [MnCl6]^(3-)** and **(c) [CoF6]^(3-)**.

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