The third ionization enthalpy is maximum for

Options

A. `Co`
B. `Ni`
C. `Mn`
D. `Zn`

Explanation

To determine which element has the maximum third ionization enthalpy among cobalt, nickel, manganese, and zinc, we need to analyze their electronic configurations and the stability of their electron arrangements.

### Step-by-Step Solution:

1. **Understanding Ionization Enthalpy**:
- Ionization enthalpy is the amount of energy required to remove an electron from an isolated gaseous atom. The third ionization enthalpy refers to the energy needed to remove the third electron.

2. **Identify the Electronic Configurations**:
- Cobalt (Co): [Ar] 3d⁷ 4s²
- Nickel (Ni): [Ar] 3d⁸ 4s²
- Manganese (Mn): [Ar] 3d⁵ 4s²
- Zinc (Zn): [Ar] 3d¹⁰ 4s²

3. **Removing Electrons**:
- When the first electron is removed, the configurations change as follows:
- Co: 3d⁷ 4s¹
- Ni: 3d⁸ 4s¹
- Mn: 3d⁵ 4s¹
- Zn: 3d¹⁰ 4s¹
- After the second electron is removed:
- Co: 3d⁶
- Ni: 3d⁷
- Mn: 3d⁵
- Zn: 3d¹⁰

4. **Analyzing the Third Ionization**:
- For the third ionization, we consider the stability of the resulting configurations:
- Co: Removing from 3d⁶ (less stable)
- Ni: Removing from 3d⁷ (less stable)
- Mn: Removing from 3d⁵ (half-filled, more stable)
- Zn: Removing from 3d¹⁰ (fully filled, very stable)

5. **Stability Considerations**:
- Half-filled (Mn) and fully filled (Zn) configurations are more stable than partially filled configurations (Co and Ni).
- Removing an electron from a fully filled orbital (Zn) requires significantly more energy due to the stability of the configuration.

6. **Conclusion**:
- Therefore, the third ionization enthalpy is maximum for Zinc (Zn) due to its fully filled d-orbital configuration, which is very stable.

### Final Answer:
The third ionization enthalpy is maximum for Zinc (Zn).