Which of the following subshells is not possible?

Options

A. 1s
B. 1p
C. 2s
D. 2p

Explanation

To determine which of the given subshells is not possible, we need to analyze each option based on the principles of quantum mechanics, specifically the quantum numbers associated with atomic orbitals.

### Step-by-Step Solution:

1. **Understanding Quantum Numbers**:
- The principal quantum number (n) indicates the shell or energy level of an electron.
- The azimuthal quantum number (l) defines the subshell and can take values from 0 to (n-1).
- For example, if n = 1, l can only be 0 (which corresponds to the s subshell).

2. **Analyzing Each Option**:
- **Option A: 1s**
- Here, n = 1 and l = 0 (s subshell).
- This is valid because l can be 0 when n = 1.
- **Option B: 1p**
- Here, n = 1 and l = 1 (p subshell).
- This is **not valid** because l cannot be equal to or greater than n. For n = 1, l can only be 0.
- **Option C: 2s**
- Here, n = 2 and l = 0 (s subshell).
- This is valid because l can be 0 when n = 2.
- **Option D: 2p**
- Here, n = 2 and l = 1 (p subshell).
- This is valid because l can be 1 when n = 2.

3. **Conclusion**:
- The only subshell that is not possible is **1p** (Option B).

### Final Answer:
**The subshell that is not possible is 1p (Option B).**