Assertion : In hydrogen and hydrogen like species, orbital energy depends only on the quantum number n whereas in multi-electron atoms it depends on quantum numbers n and l.
Reason : The principle quantum number determines the size and the energy of the orbital.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

To analyze the given assertion and reason, we will break down the statements and evaluate their correctness step by step.

### Step 1: Understanding the Assertion
**Assertion:** In hydrogen and hydrogen-like species, orbital energy depends only on the quantum number n, whereas in multi-electron atoms it depends on quantum numbers n and l.

- **Hydrogen and Hydrogen-like Species:** These species have only one electron. The energy levels are determined solely by the principal quantum number (n). This is because there are no electron-electron interactions that would cause the energy levels to vary based on other quantum numbers.

- **Multi-electron Atoms:** In contrast, multi-electron atoms have more than one electron. In these cases, both the principal quantum number (n) and the azimuthal quantum number (l) influence the energy levels due to electron-electron repulsions and shielding effects.

**Conclusion for Assertion:** The assertion is true.

### Step 2: Understanding the Reason
**Reason:** The principal quantum number determines the size and the energy of the orbital.

- The principal quantum number (n) indeed determines the size of the orbital and the energy level of the electron in that orbital. As n increases, the size of the orbital increases, and the energy of the electron also increases.

**Conclusion for Reason:** The reason is also true.

### Step 3: Evaluating the Relationship
- While both the assertion and the reason are true, the reason does not directly explain why the orbital energy in hydrogen and hydrogen-like species depends only on n, while in multi-electron atoms it depends on both n and l. The assertion focuses on the differences in energy dependency due to the number of electrons, while the reason discusses the general role of n in determining size and energy.

### Final Conclusion
- Both the assertion and reason are true, but the reason is not the correct explanation of the assertion. Therefore, the correct answer is that both the assertion and reason are true, but the reason does not correctly explain the assertion.

### Answer:
Option 2: Both assertion and reason are true, but reason is not the correct explanation of assertion.

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