Which of the following is/are inner orbital complex as well as dimagnetic in nature :
[Atomic no. `toCr=24, Mn=25, Fe=26, Co=27`]

Options

A. `[Zn(NH_(3))_(6)]^(2+)`
B. `[Ni(NH_(3))_(6)]^(2+)`
C. `[Cr(NH_(3))_(6)]^(3+)`
D. `[Co(NH_(3))_(6)]^(3+)`

Explanation

To determine which of the given complexes is an inner orbital complex and is also diamagnetic in nature, we need to analyze the electronic configurations of the metal ions in their respective oxidation states and how they interact with the strong field ligand NH3.

### Step-by-Step Solution:

1. **Identify the Metal Ions and Their Oxidation States:**
- Chromium (Cr) - Atomic number 24
- Manganese (Mn) - Atomic number 25
- Iron (Fe) - Atomic number 26
- Cobalt (Co) - Atomic number 27

2. **Determine the Electronic Configuration in the Given Oxidation States:**
- **Zinc (Zn²⁺)**:
- Atomic number = 30
- Electronic configuration of Zn: [Ar] 3d¹⁰ 4s²
- For Zn²⁺: [Ar] 3d¹⁰ (no inner orbital complex)
- **Nickel (Ni²⁺)**:
- Atomic number = 28
- Electronic configuration of Ni: [Ar] 3d⁸ 4s²
- For Ni²⁺: [Ar] 3d⁸ (no inner orbital complex)
- **Chromium (Cr³⁺)**:
- Atomic number = 24
- Electronic configuration of Cr: [Ar] 4s¹ 3d⁵
- For Cr³⁺: [Ar] 3d³ (can form an inner orbital complex)
- **Cobalt (Co³⁺)**:
- Atomic number = 27
- Electronic configuration of Co: [Ar] 4s² 3d⁷
- For Co³⁺: [Ar] 3d⁶ (can form an inner orbital complex)

3. **Determine the Type of Complex Formed:**
- **Zinc**: Forms an outer orbital complex (3d¹⁰).
- **Nickel**: Forms an outer orbital complex (3d⁸).
- **Chromium**: Forms an inner orbital complex (3d³) but is paramagnetic (has unpaired electrons).
- **Cobalt**: Forms an inner orbital complex (3d⁶) and is diamagnetic (all electrons are paired).

4. **Conclusion:**
- The only metal ion that forms an inner orbital complex and is also diamagnetic is **Cobalt (Co³⁺)**.

### Final Answer:
Cobalt (Co³⁺) with NH₃ forms an inner orbital complex and is diamagnetic in nature.

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