Which one of the following electronic configuration of an atom has the highest ionisation energy?

Options

A. `1s^(2),2s^(2)2p^(3)`
B. `1s^(2),2s^(2)2p^(6),3s^(1)`
C. `1s^(2),2s^(2)2p^(6)`
D. `1s^(2),2s^(2)2p^(5)`

Answer

To determine which electronic configuration has the highest ionization energy, we need to analyze the stability of the configurations provided. Ionization energy is the energy required to remove an electron from an atom. Generally, the more stable the electron configuration, the higher the ionization energy.

### Step-by-Step Solution:

1. **Identify the Electronic Configurations**:
Let's assume the electronic configurations given are:
- A: 2p³
- B: 3s¹
- C: 2p⁶
- D: 2p⁵

2. **Analyze Each Configuration**:
- **A: 2p³**: This configuration is half-filled. Half-filled orbitals are relatively stable due to symmetry and exchange energy. However, it is not the most stable configuration.
- **B: 3s¹**: This configuration has one electron in the outermost shell. Being in the third period, it is farther from the nucleus, and since it is unpaired, it is easier to remove this electron. Therefore, it has a lower ionization energy.
- **C: 2p⁶**: This configuration is fully filled. Fully filled orbitals are very stable and have a high ionization energy because it is difficult to remove an electron from a stable noble gas configuration.
- **D: 2p⁵**: This configuration has one unpaired electron. While it is relatively stable, it is less stable than a fully filled configuration, making it easier to remove the unpaired electron compared to a fully filled orbital.

3. **Determine the Highest Ionization Energy**:
- Comparing the stability of the configurations, the fully filled configuration (C: 2p⁶) is the most stable. Therefore, it will have the highest ionization energy since it is the most difficult to remove an electron from a stable noble gas configuration.

4. **Conclusion**:
The electronic configuration with the highest ionization energy is **C: 2p⁶**.

### Final Answer:
**C: 2p⁶** has the highest ionization energy.