Which of the following electronic configuration is not possible ?

Options

A. `2p^3`
B. `2d^6`
C. `4s^1`
D. `5f^8`

Answer

To determine which electronic configuration is not possible, we need to analyze the given configurations based on the rules of quantum numbers.

### Step-by-Step Solution:

1. **Understanding Quantum Numbers**:
- The principal quantum number (n) indicates the energy level of an electron in an atom.
- The azimuthal quantum number (l) determines the shape of the orbital and can take values from 0 to n-1.
- The magnetic quantum number (m) can take values from -l to +l.

2. **Analyzing Each Configuration**:
- **Configuration 1: 2p³**
- For n = 2, l can be 0 (s) or 1 (p).
- Since l = 1 for p, m can be -1, 0, +1.
- This configuration is possible as it fits within the quantum number rules.

- **Configuration 2: 2d⁶**
- For n = 2, l can only be 0 (s) or 1 (p).
- The d subshell (l = 2) cannot exist for n = 2, as l must be less than n.
- Therefore, this configuration is **not possible**.

- **Configuration 3: 4s¹**
- For n = 4, l can be 0 (s), 1 (p), 2 (d), or 3 (f).
- The s subshell (l = 0) is valid for n = 4.
- This configuration is possible.

- **Configuration 4: 5f⁸**
- For n = 5, l can be 0 (s), 1 (p), 2 (d), 3 (f), or 4 (g).
- The f subshell (l = 3) is valid for n = 5.
- This configuration is also possible.

3. **Conclusion**:
- The only configuration that is not possible is **2d⁶**.

### Final Answer:
The electronic configuration that is not possible is **2d⁶**.