Two electrons present in M shell will differ in

Options

A. principal quantum number
B. azimuthal quantum number
C. magnetic quantum number
D. spin quantum number

Explanation

To solve the question "Two electrons present in M shell will differ in," we need to analyze the quantum numbers associated with electrons in the M shell.

### Step-by-Step Solution:

1. **Understand the M Shell**:
- The M shell corresponds to the principal quantum number \( n = 3 \). This shell can hold a maximum of 18 electrons.

2. **Identify Quantum Numbers**:
- Electrons in an atom are described by four quantum numbers:
- Principal quantum number (\( n \)): Indicates the shell.
- Azimuthal quantum number (\( l \)): Indicates the subshell (s, p, d, f).
- Magnetic quantum number (\( m_l \)): Indicates the orientation of the orbital.
- Spin quantum number (\( m_s \)): Indicates the spin of the electron.

3. **Analyze the Options**:
- **Principal Quantum Number**: For both electrons in the M shell, \( n \) is the same (3). Thus, they do not differ in this quantum number.
- **Azimuthal Quantum Number**: The M shell can have \( l = 0 \) (s), \( l = 1 \) (p), and \( l = 2 \) (d). If both electrons are in the same subshell, they will have the same \( l \) value. Thus, they do not necessarily differ in this quantum number.
- **Magnetic Quantum Number**: This number can vary depending on the orientation of the orbital within a subshell. However, if both electrons are in the same orbital, they will have the same \( m_l \) value. Thus, they do not necessarily differ in this quantum number.
- **Spin Quantum Number**: According to Pauli's exclusion principle, no two electrons can have the same set of quantum numbers. Therefore, if both electrons are in the same orbital, they must have opposite spins. This means their spin quantum numbers will differ (one will be +1/2 and the other -1/2).

4. **Conclusion**:
- The two electrons present in the M shell will differ in their **spin quantum number**.

### Final Answer:
The two electrons present in the M shell will differ in **spin quantum number**.

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