Which is not in accordance to Aufbau principle

Options

A.
B.
C.
D.

Explanation

To determine which option is not in accordance with the Aufbau principle, we need to understand the principle itself. The Aufbau principle states that electrons fill atomic orbitals in order of increasing energy levels, starting from the lowest energy level to the highest.

### Step-by-Step Solution:

1. **Understanding the Aufbau Principle**:
- Electrons are added to the atomic orbitals starting from the lowest energy orbital to the highest. The order of filling is based on the increasing energy levels of the orbitals.

2. **Identifying the Order of Orbital Filling**:
- The order of filling orbitals is as follows:
- 1s
- 2s
- 2p
- 3s
- 3p
- 4s
- 3d
- 4p
- 5s
- 4d
- 5p
- 6s
- 4f
- 5d
- 6p
- 7s
- 5f
- 6d
- 7p

3. **Analyzing Given Options**:
- Let's analyze the given electron configurations:
- **Option A**: 2S2, 2P4 - This is correct as 2S is filled before 2P.
- **Option B**: 2S2, 2P5 - This is also correct as 2S is filled before 2P.
- **Option C**: 2S1, 2P4 - This is incorrect because 2S should be filled completely (2 electrons) before any electrons are placed in 2P.
- **Option D**: 2S2, 2P3 - This is correct as 2S is filled before 2P.

4. **Conclusion**:
- The option that is not in accordance with the Aufbau principle is **Option C (2S1, 2P4)** because it violates the rule of filling the lower energy orbital (2S) completely before moving to the higher energy orbital (2P).

### Final Answer:
- **Option C (2S1, 2P4) is not in accordance with the Aufbau principle.**