Which of the following is an inner orbital complex as well as diamagnetic in behaviour
[Atomic numbers Zn = 30, Cr = 24, Co = 27, Ni = 28.]

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 also exhibits diamagnetic behavior, we need to analyze the electronic configurations and the nature of the complexes formed by the given transition metals.

### Step-by-Step Solution:

1. **Identify the Transition Metals**:
The given atomic numbers correspond to the following elements:
- Zn (Z=30): Zinc
- Cr (Z=24): Chromium
- Co (Z=27): Cobalt
- Ni (Z=28): Nickel

2. **Determine the Electronic Configurations**:
- **Zn**: [Ar] 3d^10 4s^2
- **Cr**: [Ar] 3d^5 4s^1
- **Co**: [Ar] 3d^7 4s^2
- **Ni**: [Ar] 3d^8 4s^2

3. **Identify the Oxidation States**:
- Zinc typically exhibits a +2 oxidation state (Zn^2+), resulting in [Ar] 3d^10.
- Chromium can exhibit multiple oxidation states, but in complexes, it often shows +3 (Cr^3+) or +6 (Cr^6+).
- Cobalt commonly shows +2 (Co^2+) and +3 (Co^3+) oxidation states.
- Nickel usually shows +2 (Ni^2+) oxidation state.

4. **Determine the Type of Complexes**:
- **Inner Orbital Complex**: This refers to complexes where the d-orbitals involved in bonding are from the inner d-subshell (n-1). For example, 4d or 5d orbitals in coordination complexes of transition metals.
- **Outer Orbital Complex**: This refers to complexes where the d-orbitals involved are from the outer d-subshell (n).

5. **Analyze Diamagnetism**:
- A complex is diamagnetic if all electrons are paired. This occurs when there are no unpaired electrons in the d-orbitals.
- Zn^2+ has a completely filled d-subshell (3d^10), which means it is diamagnetic.
- Cr^3+ has 3 unpaired electrons (3d^3), Co^2+ has 3 unpaired electrons (3d^7), and Ni^2+ has 2 unpaired electrons (3d^8).

6. **Conclusion**:
- Among the given options, **Zn** is the only metal that forms an inner orbital complex (due to its filled d-orbitals) and is also diamagnetic (since it has no unpaired electrons).

### Final Answer:
**Zinc (Zn)** is an inner orbital complex and is diamagnetic in behavior.