Four successive members of the first row transition elements are listed below with their atomic number. Which one of them is expected to have the highest third ionisation enthalpy ?

Options

A. Vanadium (Z - 23)
B. Manganese (Z = 25)
C. Chromium (Z =24)
D. Iron (Z=26)

Answer

To determine which of the four successive members of the first row transition elements has the highest third ionization enthalpy, we need to analyze the electronic configurations of the given elements and understand the concept of ionization enthalpy.

### Step-by-Step Solution:

1. **Identify the Elements and Their Atomic Numbers**:
- Vanadium (V) - Atomic Number: 23
- Chromium (Cr) - Atomic Number: 24
- Manganese (Mn) - Atomic Number: 25
- Iron (Fe) - Atomic Number: 26

2. **Write the Electronic Configurations**:
- Vanadium (V): [Ar] 3d³ 4s²
- Chromium (Cr): [Ar] 3d⁵ 4s¹
- Manganese (Mn): [Ar] 3d⁵ 4s²
- Iron (Fe): [Ar] 3d⁶ 4s²

3. **Understand Ionization Enthalpy**:
- Ionization enthalpy is the energy required to remove an electron from an atom in the gas phase.
- The third ionization enthalpy refers to the energy required to remove the third electron from the atom.

4. **Determine the Electron Removal Order**:
- For Vanadium (3d³), removing the third electron will come from the 3d subshell.
- For Chromium (3d⁵), removing the third electron will also come from the 3d subshell, but it is a half-filled configuration, which is more stable.
- For Manganese (3d⁵), the third electron will also be removed from the 3d subshell, and it has a stable half-filled configuration.
- For Iron (3d⁶), the third electron will be removed from the 3d subshell, but it is less stable compared to the half-filled configurations.

5. **Analyze Stability and Ionization Energy**:
- Half-filled and fully filled subshells are more stable and require more energy to remove electrons.
- Manganese (Mn) has a half-filled 3d subshell (3d⁵), making it more stable and thus requiring a higher energy to remove the third electron compared to the others.

6. **Conclusion**:
- Among the four elements, Manganese (Mn) is expected to have the highest third ionization enthalpy due to its stable half-filled 3d configuration.

### Final Answer:
The element expected to have the highest third ionization enthalpy is **Manganese (Mn)**.