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. Chromium ( Z= 24)
C. Manganesc ( Z=25)
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 will analyze the electronic configurations and stability of the resulting ions after the third ionization.

### 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): \( \text{[Ar]} 4s^2 3d^3 \)
- Chromium (Cr): \( \text{[Ar]} 4s^1 3d^5 \)
- Manganese (Mn): \( \text{[Ar]} 4s^2 3d^5 \)
- Iron (Fe): \( \text{[Ar]} 4s^2 3d^6 \)

3. **Determine the Configuration After Each Ionization**:
- **Vanadium**:
- \( V \rightarrow V^+ \): \( \text{[Ar]} 4s^1 3d^3 \)
- \( V^+ \rightarrow V^{2+} \): \( \text{[Ar]} 3d^3 \)
- \( V^{2+} \rightarrow V^{3+} \): \( \text{[Ar]} 3d^2 \)
- **Chromium**:
- \( Cr \rightarrow Cr^+ \): \( \text{[Ar]} 4s^0 3d^5 \)
- \( Cr^+ \rightarrow Cr^{2+} \): \( \text{[Ar]} 3d^4 \)
- \( Cr^{2+} \rightarrow Cr^{3+} \): \( \text{[Ar]} 3d^3 \)
- **Manganese**:
- \( Mn \rightarrow Mn^+ \): \( \text{[Ar]} 4s^2 3d^4 \)
- \( Mn^+ \rightarrow Mn^{2+} \): \( \text{[Ar]} 4s^1 3d^5 \)
- \( Mn^{2+} \rightarrow Mn^{3+} \): \( \text{[Ar]} 3d^4 \)
- **Iron**:
- \( Fe \rightarrow Fe^+ \): \( \text{[Ar]} 4s^1 3d^6 \)
- \( Fe^+ \rightarrow Fe^{2+} \): \( \text{[Ar]} 4s^0 3d^6 \)
- \( Fe^{2+} \rightarrow Fe^{3+} \): \( \text{[Ar]} 3d^5 \)

4. **Analyze Stability of the Resulting Ions**:
- The stability of the resulting ions after the third ionization is crucial.
- **Mn²⁺** has a half-filled \( 3d^5 \) configuration, which is particularly stable.
- **Fe³⁺** has a \( 3d^5 \) configuration as well, but it is less stable than Mn²⁺ due to the higher positive charge.
- **Cr³⁺** and **V³⁺** have configurations that are less stable compared to Mn²⁺.

5. **Conclusion**:
- Since Mn²⁺ has the most stable electronic configuration after the second ionization, it will experience the highest third ionization enthalpy. Therefore, the element expected to have the highest third ionization enthalpy is **Manganese (Mn)**.

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

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