Which one of the following ions has electronic configuration `[Ar]3d^(6)` ? `(At. Nos. Mn = 25, Fe = 26, Co = 27, Ni = 28)`

Options

A. `Ni^(3+)`
B. `Mn^(3+)`
C. `Fe^(3+)`
D. `Co^(3+)`

Explanation

To determine which ion has the electronic configuration of \([Ar] 3d^6\), we will analyze the electronic configurations of the given elements and their corresponding ions.

### Step 1: Identify the atomic numbers and electronic configurations of the elements.
- **Manganese (Mn)**: Atomic number = 25
- Electronic configuration: \([Ar] 3d^5 4s^2\)

- **Iron (Fe)**: Atomic number = 26
- Electronic configuration: \([Ar] 3d^6 4s^2\)

- **Cobalt (Co)**: Atomic number = 27
- Electronic configuration: \([Ar] 3d^7 4s^2\)

- **Nickel (Ni)**: Atomic number = 28
- Electronic configuration: \([Ar] 3d^8 4s^2\)

### Step 2: Determine the electronic configurations of the ions.
We need to remove electrons from the outermost shell (4s and then 3d) to find the electronic configurations of the ions.

1. **Manganese ion (Mn³⁺)**:
- Remove 3 electrons from \([Ar] 3d^5 4s^2\):
- \([Ar] 3d^4 4s^0\)

2. **Iron ion (Fe³⁺)**:
- Remove 3 electrons from \([Ar] 3d^6 4s^2\):
- \([Ar] 3d^5 4s^0\)

3. **Cobalt ion (Co³⁺)**:
- Remove 3 electrons from \([Ar] 3d^7 4s^2\):
- \([Ar] 3d^6 4s^0\)

4. **Nickel ion (Ni³⁺)**:
- Remove 3 electrons from \([Ar] 3d^8 4s^2\):
- \([Ar] 3d^7 4s^0\)

### Step 3: Compare the configurations.
Now we compare the configurations of the ions we calculated:
- **Mn³⁺**: \([Ar] 3d^4\)
- **Fe³⁺**: \([Ar] 3d^5\)
- **Co³⁺**: \([Ar] 3d^6\)
- **Ni³⁺**: \([Ar] 3d^7\)

### Conclusion:
The ion that has the electronic configuration of \([Ar] 3d^6\) is **Co³⁺ (Cobalt ion)**.

### Final Answer:
**Cobalt (Co³⁺)** has the electronic configuration \([Ar] 3d^6\).

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