How many subshells are there in the M shell?A.) 4B.) 3C.) 6D.) 5

To determine how many subshells are present in the M shell, we can refer to the principles of quantum mechanics related to atomic structure.

1. **Understanding Shells and Subshells**:
- Electron shells are designated by principal quantum numbers \( n \) (where \( n = 1, 2, 3, \ldots \)).
- Each shell can contain one or more subshells, designated by the angular momentum quantum number \( l \).

2. **Subshell Designations**:
- The subshells are denoted as:
- \( s \) (where \( l = 0 \))
- \( p \) (where \( l = 1 \))
- \( d \) (where \( l = 2 \))
- \( f \) (where \( l = 3 \))
- The maximum value of \( l \) for a given principal quantum number \( n \) is \( n - 1 \).

3. **Determining Subshells in the M Shell**:
- For the M shell, \( n = 3 \).
- The possible values of \( l \) are \( 0, 1, 2 \):
- \( l = 0 \): \( s \) subshell
- \( l = 1 \): \( p \) subshell
- \( l = 2 \): \( d \) subshell
- Thus, the M shell contains the following subshells:
- \( 3s \)
- \( 3p \)
- \( 3d \)

4. **Counting the Subshells**:
- Therefore, the M shell has **3 subshells**: \( s, p, \) and \( d \).

### Answer:
**B.) 3**