Assertion : Noble gases have positive electron gain enthalpy.
Reason : Noble gases have stable closed shell electronic configuration.

Options

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

Answer

To solve the question, we need to analyze the assertion and the reason provided:

**Assertion:** Noble gases have positive electron gain enthalpy.
**Reason:** Noble gases have stable closed shell electronic configuration.

### Step-by-Step Solution:

1. **Understanding Electron Gain Enthalpy:**
- Electron gain enthalpy is the amount of energy released or absorbed when an electron is added to a neutral atom in the gaseous state. A positive electron gain enthalpy indicates that energy is required to add an electron to the atom.

2. **Analyzing Noble Gases:**
- Noble gases (like Helium, Neon, Argon, etc.) have a complete outer shell of electrons. For example, Helium has 2 electrons (1s²), Neon has 10 electrons (1s² 2s² 2p⁶), and Argon has 18 electrons (1s² 2s² 2p⁶ 3s² 3p⁶). This configuration is known as a stable closed shell.

3. **Stability of Noble Gases:**
- The stable closed shell configuration means that noble gases are already in a low-energy state. They do not tend to gain or lose electrons easily because they are stable as they are.

4. **Implication of Stability on Electron Gain Enthalpy:**
- Since noble gases are stable and do not readily accept additional electrons, it requires energy to force an electron onto them. This results in a positive electron gain enthalpy, meaning that energy must be supplied to add an electron.

5. **Conclusion:**
- Both the assertion and the reason are true. The reason correctly explains why noble gases have a positive electron gain enthalpy due to their stable closed shell electronic configuration.

### Final Answer:
- Assertion: True
- Reason: True
- The reason is the correct explanation of the assertion.