Which has the highest second ionisation potential ?

Options

A. Nitrogen
B. Carbon
C. Oxygen
D. Fluorine

Answer

To determine which element has the highest second ionization potential, we will follow these steps:

### Step 1: Identify the Elements and Their Electronic Configurations
We start by identifying the elements in question and writing their electronic configurations. The elements are typically from groups in the periodic table, and their configurations are as follows:
- Nitrogen (N): 1s² 2s² 2p³
- Carbon (C): 1s² 2s² 2p²
- Oxygen (O): 1s² 2s² 2p⁴
- Fluorine (F): 1s² 2s² 2p⁵

### Step 2: Understand Second Ionization Potential
Second ionization potential refers to the energy required to remove a second electron from a singly charged ion. For example, if we take nitrogen (N) and remove one electron, we get N⁺ with the configuration 1s² 2s² 2p². The second ionization potential is the energy needed to remove another electron from this ion.

### Step 3: Remove One Electron from Each Configuration
Now, we will remove one electron from each of the configurations to find the resulting configurations:
- For Nitrogen (N): 1s² 2s² 2p³ → N⁺: 1s² 2s² 2p²
- For Carbon (C): 1s² 2s² 2p² → C⁺: 1s² 2s² 2p¹
- For Oxygen (O): 1s² 2s² 2p⁴ → O⁺: 1s² 2s² 2p³
- For Fluorine (F): 1s² 2s² 2p⁵ → F⁺: 1s² 2s² 2p⁴

### Step 4: Analyze the Stability of the Resulting Configurations
Next, we analyze the stability of the resulting configurations after the removal of the second electron:
- N⁺ (1s² 2s² 2p²): Has a stable half-filled p subshell.
- C⁺ (1s² 2s² 2p¹): Less stable due to a partially filled p subshell.
- O⁺ (1s² 2s² 2p³): Also has a stable half-filled p subshell.
- F⁺ (1s² 2s² 2p⁴): Less stable due to a partially filled p subshell.

### Step 5: Determine Which Has the Highest Second Ionization Potential
The stability of the resulting configurations indicates that it is more difficult to remove an electron from a stable configuration. Therefore, the elements with half-filled p subshells (N⁺ and O⁺) will have higher second ionization potentials compared to those with partially filled subshells (C⁺ and F⁺).

Among these, Oxygen (O) has a higher second ionization potential than Nitrogen (N) due to its higher effective nuclear charge and the stability of the half-filled p subshell.

### Conclusion
Thus, the element with the highest second ionization potential is **Oxygen (O)**.

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