Which of the following has highest second ionization energy ?

Options

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

Explanation

To determine which of the given elements has the highest second ionization energy, we will analyze the electron configurations and the stability of the resulting ions after the removal of electrons. The elements in question are Nickel (Ni), Vanadium (V), Chromium (Cr), and Manganese (Mn).

### Step 1: Understand Ionization Energy
Ionization energy is the energy required to remove an electron from an isolated atom. The second ionization energy specifically refers to the energy needed to remove a second electron after the first has already been removed.

### Step 2: Electron Configurations
We will write the electron configurations for each element:

1. **Nickel (Ni)**: Atomic number = 28
- Electron Configuration: [Ar] 3d⁸ 4s²
2. **Vanadium (V)**: Atomic number = 23
- Electron Configuration: [Ar] 3d³ 4s²
3. **Chromium (Cr)**: Atomic number = 24
- Electron Configuration: [Ar] 3d⁵ 4s¹
4. **Manganese (Mn)**: Atomic number = 25
- Electron Configuration: [Ar] 3d⁵ 4s²

### Step 3: Analyze Second Ionization Energy
- **Nickel (Ni)**:
- First ionization removes one of the 4s electrons, resulting in [Ar] 3d⁸.
- The second ionization will remove an electron from the 3d orbital, which is more stable. Thus, the second ionization energy is relatively low.

- **Vanadium (V)**:
- First ionization removes one of the 4s electrons, resulting in [Ar] 3d³.
- The second ionization will also remove another 4s electron, which is less stable. Hence, the second ionization energy is not very high.

- **Chromium (Cr)**:
- First ionization removes the 4s electron, resulting in [Ar] 3d⁵.
- The second ionization will remove one of the 3d electrons. Since the 3d⁵ configuration is stable (half-filled), removing an electron from here requires a significant amount of energy. Thus, the second ionization energy is high.

- **Manganese (Mn)**:
- First ionization removes one of the 4s electrons, resulting in [Ar] 3d⁵.
- The second ionization will remove another 4s electron, which is less stable. Therefore, the second ionization energy is lower than that of Chromium.

### Step 4: Conclusion
Among the four elements, Chromium has the highest second ionization energy because removing an electron from the stable half-filled 3d subshell requires significantly more energy compared to the others.

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