Which electronic configuration does not follow the Aufbau rule? 

Options

A. `1s^2, 2s^2, 2p^6`
B. `1s^2,2s^2, 2p^4, 3s^2`
C. `1s^2`
D. `1s^2, 2s^2, 2p^6, 3s^2`

Answer

To determine which electronic configuration does not follow the Aufbau principle, we need to analyze each provided configuration step by step.

### Step-by-Step Solution:

1. **Understand the Aufbau Principle**: The Aufbau principle states that electrons occupy the lowest energy orbitals first before moving to higher energy orbitals. The order of filling is typically: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc.

2. **Analyze the Given Configurations**: We will evaluate the provided electronic configurations one by one to see if they adhere to the Aufbau principle.

3. **Configuration 1: 1s² 2s² 2p⁶**
- This configuration is correct. The 1s orbital is filled first (2 electrons), followed by the 2s orbital (2 electrons), and then the 2p orbital (6 electrons). This follows the Aufbau principle.

4. **Configuration 2: 1s² 2s² 2p⁴ 3s²**
- This configuration is incorrect. According to the Aufbau principle, the 2p orbital should be filled with a maximum of 6 electrons before moving to the 3s orbital. Here, the 2p orbital has only 4 electrons, meaning it is not fully filled, which violates the principle.

5. **Configuration 3: 1s² 2s² 2p⁶ 3s²**
- This configuration is correct. The 1s, 2s, and 2p orbitals are fully filled before moving to the 3s orbital, which is filled with 2 electrons. This follows the Aufbau principle.

6. **Configuration 4: 1s² 2s² 2p⁶ 3s² 3p⁶**
- This configuration is also correct. The 1s, 2s, 2p, and 3s orbitals are fully filled before moving to the 3p orbital, which is filled with 6 electrons. This adheres to the Aufbau principle.

7. **Conclusion**: The configuration that does not follow the Aufbau principle is **1s² 2s² 2p⁴ 3s²**.

### Final Answer:
The electronic configuration that does not follow the Aufbau rule is **1s² 2s² 2p⁴ 3s²**.