Which one of the following subshells is not compatible with a principal quantum number of `n=4`?

Options

A. s
B. d
C. g
D. p

Answer

To determine which subshell is not compatible with a principal quantum number of \( n = 4 \), we need to understand the relationship between the principal quantum number and the subshells.

### Step-by-Step Solution:

1. **Understanding Principal Quantum Number (n)**:
- The principal quantum number \( n \) indicates the shell or energy level of an electron in an atom. The value of \( n \) can be any positive integer (1, 2, 3, ...).

2. **Identifying Subshells**:
- For each principal quantum number \( n \), there are specific subshells associated with it:
- \( n = 1 \): Subshells = 1s
- \( n = 2 \): Subshells = 2s, 2p
- \( n = 3 \): Subshells = 3s, 3p, 3d
- \( n = 4 \): Subshells = 4s, 4p, 4d, 4f

3. **Listing Subshells for \( n = 4 \)**:
- For \( n = 4 \), the compatible subshells are:
- 4s (l = 0)
- 4p (l = 1)
- 4d (l = 2)
- 4f (l = 3)

4. **Identifying the Incompatible Subshell**:
- The subshells that can exist for \( n = 4 \) are s, p, d, and f. However, there is no subshell called g for \( n = 4 \).
- The g subshell corresponds to \( l = 4 \), which can only exist when \( n \) is 5 or higher.

5. **Conclusion**:
- Therefore, the subshell that is not compatible with a principal quantum number of \( n = 4 \) is **g**.

### Final Answer:
The subshell that is not compatible with a principal quantum number of \( n = 4 \) is **g**.