The atomic numbers of vanadium (V), chromium (Cr), manganese (Mn) and iron (Fe) are respectively 23, 24, 25 and 26. Which one of these may be expected to have the highest second ionisation enthalpy ?
V
Cr
Mn
Fe

Options

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

Explanation

To determine which element among vanadium (V), chromium (Cr), manganese (Mn), and iron (Fe) has the highest second ionization enthalpy, we can follow these steps:

### Step 1: Write 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

### Step 2: Remove one electron to find the first ionization state
- For Vanadium (V): After removing one electron, configuration becomes [Ar] 3d³ 4s¹
- For Chromium (Cr): After removing one electron, configuration becomes [Ar] 3d⁵ 4s⁰
- For Manganese (Mn): After removing one electron, configuration becomes [Ar] 3d⁵ 4s¹
- For Iron (Fe): After removing one electron, configuration becomes [Ar] 3d⁶ 4s¹

### Step 3: Analyze the stability of the resulting configurations
- Chromium (Cr) has a half-filled d-subshell (3d⁵), which is particularly stable. Removing a second electron from this stable configuration would require significantly more energy.
- Vanadium (V) and Manganese (Mn) have less stable configurations after the first ionization, as they do not have a half-filled d-subshell.
- Iron (Fe) has a filled 4s subshell and a partially filled d-subshell, but it is less stable compared to the half-filled d-subshell of chromium.

### Step 4: Determine the element with the highest second ionization enthalpy
Based on the stability of the resulting electronic configurations after the first ionization, chromium (Cr) is expected to have the highest second ionization enthalpy due to the extra stability of its half-filled d-subshell.

### Final Answer
The element expected to have the highest second ionization enthalpy is **Chromium (Cr)**.

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