Which of the following violates the Aufbau principal ?

Options

A.
B.
C.
D.

Answer

To determine which option violates the Aufbau principle, we need to understand the principle itself and how it applies to electron configuration.

### Step-by-Step Solution:

1. **Understand the Aufbau Principle**:
- The Aufbau principle states that electrons fill atomic orbitals in order of increasing energy levels. This means that lower energy orbitals are filled before higher energy orbitals.

2. **Identify the n + l Rule**:
- The n + l rule helps to determine the order of filling. Here, 'n' is the principal quantum number (energy level), and 'l' is the azimuthal quantum number (subshell).
- For example, for the 2s subshell, n = 2 and l = 0, thus n + l = 2. For the 2p subshell, n = 2 and l = 1, thus n + l = 3.

3. **Compare Energy Levels**:
- According to the n + l rule, the 2s orbital (n + l = 2) has a lower energy than the 2p orbital (n + l = 3). Therefore, the 2s orbital must be filled before the 2p orbital.

4. **Analyze the Given Options**:
- Check the electron configurations provided in the options.
- If any option shows that the 2p orbital is filled before the 2s orbital, or if the 2s orbital has fewer than 2 electrons while the 2p has electrons, that option would violate the Aufbau principle.

5. **Identify the Violation**:
- If one of the options shows that the 2s subshell has only 1 electron while the 2p subshell has electrons, this violates the Aufbau principle because the 2s should be fully filled (2 electrons) before any electrons are placed in the 2p subshell.

### Conclusion:
- The option that shows the 2s subshell with fewer than 2 electrons while the 2p subshell has electrons violates the Aufbau principle.