Which of the following electronic configuration is incorrect ?

Options

A. `1s^2,2s^2,2p_x^2 ,2p_y^2 , 2p_z ^2 , 3s ^2 , 3p_x ^1`
B. `1s^(2) , 2s^(1),2p_(x)^(1),2p_(y)^(1) , 2p_(z)^(1)`
C. `1s^(2),2s^(2),2p^(6),3s^(2),3p^(6) , 3d^(5),4s^(2)`
D. `1s^(2) , 2s^(2),2p^(6) , 3s^(2),3p_(x)^(1) ,3p_(y) ^(1) , 3p_(z)^(1)`

Answer

To determine which electronic configuration is incorrect, we need to analyze each option based on the Aufbau Principle and the n + l rule. The Aufbau Principle states that electrons fill atomic orbitals in order of increasing energy, and the n + l rule helps us compare the energy levels of orbitals.

### Step-by-Step Solution:

1. **Understand the Aufbau Principle**:
- The Aufbau Principle states that electrons fill the lowest energy orbitals first before moving to higher energy levels.

2. **Apply the n + l Rule**:
- The n + l rule helps determine the order of filling. For each orbital, calculate n + l, where n is the principal quantum number and l is the azimuthal quantum number.
- The lower the n + l value, the lower the energy of the orbital. If two orbitals have the same n + l value, the one with the lower n value is filled first.

3. **Analyze Each Configuration**:
- **Option 1**: 1s², 2s², 2p², 3s², 3px¹
- n + l values:
- 1s: n=1, l=0 → 1 + 0 = 1
- 2s: n=2, l=0 → 2 + 0 = 2
- 2p: n=2, l=1 → 2 + 1 = 3
- 3s: n=3, l=0 → 3 + 0 = 3
- This configuration follows the Aufbau Principle correctly.

- **Option 2**: 1s², 2s¹, 2p, 2px¹, 2py¹, 2pz¹
- Here, 2s is not completely filled (it can hold 2 electrons), but electrons are being placed in 2p before 2s is filled. This violates the Aufbau Principle.
- Therefore, this configuration is **incorrect**.

- **Option 3**: 1s², 2s², 2p⁶, 3s², 3p⁶
- n + l values:
- 1s: n=1, l=0 → 1
- 2s: n=2, l=0 → 2
- 2p: n=2, l=1 → 3
- 3s: n=3, l=0 → 3
- 3p: n=3, l=1 → 4
- This configuration follows the Aufbau Principle correctly.

- **Option 4**: 1s², 2s², 2p⁶, 3s², 3px¹, 3py¹, 3pz¹
- n + l values:
- 1s: n=1, l=0 → 1
- 2s: n=2, l=0 → 2
- 2p: n=2, l=1 → 3
- 3s: n=3, l=0 → 3
- 3p: n=3, l=1 → 4
- This configuration also follows the Aufbau Principle correctly.

4. **Conclusion**:
- The incorrect electronic configuration is **Option 2**: 1s², 2s¹, 2p, 2px¹, 2py¹, 2pz¹.