Assertion : Ionisation enthalpy of noble gases is zero
Reason :Noble gases have fully field valance shell

Options

A. If both (A) and (R ) are correct and (R ) is the correct explanation of (A)
B. If both (A) and (R ) are correct,but (R ) is the correct explanation of (A)
C. If (A) is correct but (R ) is incorrect
D. If (A) is incorrect but (R ) is correct

Explanation

To solve the assertion and reason question, we need to analyze both the assertion and the reason carefully.

### Step 1: Analyze the Assertion
The assertion states that "Ionisation enthalpy of noble gases is zero."

- Ionization enthalpy is the energy required to remove an electron from an atom in the gaseous state. For noble gases, this value is not zero; rather, it is very high due to their stable electron configuration. Therefore, the assertion is **incorrect**.

### Step 2: Analyze the Reason
The reason states that "Noble gases have fully filled valence shell."

- Noble gases indeed have fully filled valence shells, which contributes to their stability and high ionization enthalpy. This statement is **correct**.

### Step 3: Conclusion
Based on the analysis:
- The assertion is incorrect (it claims ionization enthalpy is zero, which is false).
- The reason is correct (noble gases have fully filled valence shells).

Thus, the correct answer is that the assertion is incorrect but the reason is correct.

### Final Answer
The answer is **Option D**: Assertion is incorrect but reason is correct.

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