No two electrons in an orbital can have parallel spin. This statement emerges from

Options

A. Hund's rule
B. Aufbau principle
C. Pauli's exclusion principle
D. (n+1) rule

Answer

To answer the question "No two electrons in an orbital can have parallel spin. This statement emerges from," we need to analyze the principles of quantum mechanics that govern electron behavior in atoms.

### Step-by-Step Solution:

1. **Understanding Electron Spin**:
- Electrons have a property called "spin," which can be thought of as a form of angular momentum. Each electron can have one of two spin states: "up" (↑) or "down" (↓).

2. **Pauli Exclusion Principle**:
- The statement in the question is fundamentally derived from the **Pauli Exclusion Principle**. This principle states that no two electrons in an atom can have the same set of four quantum numbers.
- Since the spin quantum number is one of these four quantum numbers, if two electrons were to have parallel spins (both ↑ or both ↓), they would share three quantum numbers (the principal quantum number, azimuthal quantum number, and magnetic quantum number), which violates the Pauli Exclusion Principle.

3. **Implications of the Principle**:
- As a result of the Pauli Exclusion Principle, when two electrons occupy the same orbital, they must have opposite spins. This is why we often see electron configurations written with one electron having an "up" spin and the other having a "down" spin in the same orbital.

4. **Conclusion**:
- Therefore, the statement "No two electrons in an orbital can have parallel spin" emerges from the **Pauli Exclusion Principle**.

### Final Answer:
The statement emerges from the **Pauli Exclusion Principle**.