The correct order of second ionisation potential of C, N, O and F is:

Options

A. ` C gt N gt O gt F `
B. ` O gt N gt F gtC `
C. `O gt F gt N gt C `
D. `F gt O gt N gt C `

Answer

To determine the correct order of the second ionization potential of carbon (C), nitrogen (N), oxygen (O), and fluorine (F), we will follow these steps:

### Step 1: Understand Ionization Potential
Ionization potential (or ionization energy) is the energy required to remove an electron from an atom. The second ionization potential refers to the energy required to remove a second electron after the first one has already been removed.

### Step 2: Electron Configuration
We need to consider the electron configurations of the elements:
- Carbon (C): 1s² 2s² 2p²
- Nitrogen (N): 1s² 2s² 2p³
- Oxygen (O): 1s² 2s² 2p⁴
- Fluorine (F): 1s² 2s² 2p⁵

### Step 3: First Ionization Energy
When we remove the first electron:
- C → C⁺ (removes one 2p electron, configuration becomes 1s² 2s² 2p¹)
- N → N⁺ (removes one 2p electron, configuration becomes 1s² 2s² 2p²)
- O → O⁺ (removes one 2p electron, configuration becomes 1s² 2s² 2p³)
- F → F⁺ (removes one 2p electron, configuration becomes 1s² 2s² 2p⁴)

### Step 4: Second Ionization Energy
Now we analyze the second ionization energy:
- For Carbon (C): After the first ionization, it has a configuration of 1s² 2s² 2p¹. Removing another electron from this state requires more energy due to the remaining electrons being less stable.
- For Nitrogen (N): After the first ionization, it has a configuration of 1s² 2s² 2p². The removal of an electron from a half-filled configuration (2p³) is relatively stable.
- For Oxygen (O): After the first ionization, it has a configuration of 1s² 2s² 2p³. This configuration is half-filled, which is more stable.
- For Fluorine (F): After the first ionization, it has a configuration of 1s² 2s² 2p⁴. Removing an electron from this configuration is less stable than from nitrogen or oxygen.

### Step 5: Stability Consideration
The stability of half-filled and fully filled configurations plays a crucial role:
- Half-filled configurations (like N and O after first ionization) are more stable than partially filled configurations (like C and F).
- Therefore, the second ionization potential will be highest for O, followed by N, then F, and finally C.

### Step 6: Conclusion
Based on the above analysis, the correct order of second ionization potential of C, N, O, and F is:
**O > N > F > C**