Which of the following transition metal cation has maxi- mum unpaired electrons?

Options

A. `Mn^(2+ )`
B. `Fe^(2+) `
C. `Co^(2+ )`
D. `Ni^(2+ )`

Answer

To determine which transition metal cation has the maximum number of unpaired electrons, we will analyze the electronic configurations of the given transition metal cations: manganese (Mn²⁺), iron (Fe²⁺), cobalt (Co²⁺), and nickel (Ni²⁺).

### Step-by-Step Solution:

1. **Identify the Atomic Numbers and General Configurations:**
- Manganese (Mn): Atomic number = 25, Configuration = [Ar] 4s² 3d⁵
- Iron (Fe): Atomic number = 26, Configuration = [Ar] 4s² 3d⁶
- Cobalt (Co): Atomic number = 27, Configuration = [Ar] 4s² 3d⁷
- Nickel (Ni): Atomic number = 28, Configuration = [Ar] 4s² 3d⁸

2. **Determine the Configuration After Ionization:**
- For Mn²⁺: Remove 2 electrons from 4s, so configuration becomes [Ar] 3d⁵.
- For Fe²⁺: Remove 2 electrons from 4s, so configuration becomes [Ar] 3d⁶.
- For Co²⁺: Remove 2 electrons from 4s, so configuration becomes [Ar] 3d⁷.
- For Ni²⁺: Remove 2 electrons from 4s, so configuration becomes [Ar] 3d⁸.

3. **Count the Unpaired Electrons:**
- Mn²⁺ (3d⁵): The 3d subshell has 5 electrons, all unpaired. **Unpaired Electrons = 5**
- Fe²⁺ (3d⁶): The 3d subshell has 6 electrons, with 4 unpaired (1 pair). **Unpaired Electrons = 4**
- Co²⁺ (3d⁷): The 3d subshell has 7 electrons, with 3 unpaired (2 pairs). **Unpaired Electrons = 3**
- Ni²⁺ (3d⁸): The 3d subshell has 8 electrons, with 2 unpaired (3 pairs). **Unpaired Electrons = 2**

4. **Conclusion:**
- The cation with the maximum number of unpaired electrons is Mn²⁺ with **5 unpaired electrons**.

### Final Answer:
The transition metal cation with the maximum unpaired electrons is **Mn²⁺**.