Assertion (A) : The ionisation energy of N is more than that of O
Reason (R ) : Electronic configuration of N is more stable due to half - fillied `2p` orbitals

Options

A. If both (A) and (R ) correct and (R ) is the correct explanation for (A)
B. If both (A) and (R ) correct and (R ) is the correct explanation for (A)
C. If (A) is correct but (R ) is incorrect
D. If (A) is incorrect but (R ) is correct

Explanation

To solve the assertion and reason question regarding the ionization energy of nitrogen (N) and oxygen (O), we can follow these steps:

### Step-by-Step Solution:

1. **Understand Ionization Energy**:
- Ionization energy is the energy required to remove an electron from an atom or ion. A higher ionization energy indicates that it is more difficult to remove an electron.

2. **Compare the Ionization Energies of N and O**:
- The assertion states that the ionization energy of nitrogen (N) is greater than that of oxygen (O). This is indeed true.
- Ionization energies generally increase across a period in the periodic table. However, nitrogen has a unique electronic configuration that affects its ionization energy.

3. **Write the Electronic Configurations**:
- Nitrogen (N): The electronic configuration is \(1s^2 2s^2 2p^3\).
- Oxygen (O): The electronic configuration is \(1s^2 2s^2 2p^4\).

4. **Analyze the Stability of Electronic Configurations**:
- Nitrogen has half-filled \(2p\) orbitals (3 electrons in 2p), which is a more stable configuration due to symmetry and exchange energy.
- Oxygen has one more electron in the \(2p\) orbitals, making it less stable compared to nitrogen because it does not have half-filled orbitals.

5. **Conclusion on Assertion and Reason**:
- The assertion (A) is true: The ionization energy of N is indeed greater than that of O.
- The reason (R) is also true: The electronic configuration of nitrogen is more stable due to half-filled \(2p\) orbitals.
- Therefore, both the assertion and reason are correct, and the reason correctly explains the assertion.

### Final Answer:
Both the assertion and reason are correct, and the correct answer is option number one.

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