The atomic number of `V,Cr, Mn and Fe` are respectively `23,24,25 and 26.` Which one of these may be expected to have the highest second ionization enthalpy?

Options

A. `V`
B. `Cr`
C. `Mn`
D. `Fe`

Answer

To determine which element among Vanadium (V), Chromium (Cr), Manganese (Mn), and Iron (Fe) has the highest second ionization enthalpy, we need to analyze their electronic configurations and the stability of their electron arrangements after the first ionization.

### Step-by-Step Solution:

1. **Identify the Atomic Numbers and Electronic Configurations:**
- Vanadium (V): Atomic number 23 → Electronic configuration: [Ar] 3d³ 4s²
- Chromium (Cr): Atomic number 24 → Electronic configuration: [Ar] 3d⁵ 4s¹
- Manganese (Mn): Atomic number 25 → Electronic configuration: [Ar] 3d⁵ 4s²
- Iron (Fe): Atomic number 26 → Electronic configuration: [Ar] 3d⁶ 4s²

2. **Remove One Electron to Find First Ionization:**
- After removing one electron (first ionization):
- V: [Ar] 3d³ 4s¹
- Cr: [Ar] 3d⁵ 4s⁰
- Mn: [Ar] 3d⁵ 4s¹
- Fe: [Ar] 3d⁶ 4s¹

3. **Analyze the Stability of the Remaining Electron Configurations:**
- For Chromium (Cr), after the first ionization, it has a half-filled d-subshell (3d⁵), which is particularly stable.
- For Vanadium (V), Manganese (Mn), and Iron (Fe), the remaining configurations do not have the same level of stability as Cr after the removal of the first electron.

4. **Consider the Second Ionization:**
- The second ionization enthalpy refers to the energy required to remove a second electron after the first has been removed.
- Since Chromium has a half-filled d-subshell after the first ionization, removing another electron from this stable configuration will require significantly more energy compared to the others.

5. **Conclusion:**
- Therefore, Chromium (Cr) is expected to have the highest second ionization enthalpy due to the stability of its half-filled d-subshell after the first ionization.

### Final Answer:
**Chromium (Cr) has the highest second ionization enthalpy.**