Assertion: van der Waals equation is applicable only to non-ideal gases.
Reason: Ideal gases obey the equation `PV=nRT`.

Options

A. If both assertion and reason are correct and reason is correct explanation for assertion
B. If both assertion and reason are correct and reason is not correct explanation for assertion
C. If assertion is correct but reason is incorrect
D. If assertion and reason are both incorreect.

Explanation

To solve the question, we will analyze the assertion and the reason provided, and determine their validity and relationship.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "van der Waals equation is applicable only to non-ideal gases."
- The van der Waals equation is a modified version of the ideal gas law that accounts for the interactions between gas molecules and the volume occupied by them. It is expressed as:
\[ \left(P + \frac{a n^2}{V^2}\right)(V - nB) = nRT \]
- This equation is indeed used for real gases, which do not behave ideally under all conditions. Therefore, the assertion is **true**.

2. **Understanding the Reason**:
- The reason states that "Ideal gases obey the equation \(PV = nRT\)."
- This is the fundamental equation for ideal gases, which assumes no intermolecular forces and that the volume of gas molecules is negligible. This statement is also **true**.

3. **Analyzing the Relationship**:
- The assertion and reason are both true statements, but the reason does not provide a correct explanation for the assertion.
- The assertion specifically refers to the applicability of the van der Waals equation to non-ideal gases, while the reason discusses the behavior of ideal gases, which is not directly related to why the van der Waals equation is applicable only to non-ideal gases.

4. **Conclusion**:
- Since both the assertion and reason are true but the reason does not explain the assertion, the correct answer is that the assertion is true, the reason is true, but the reason is not a correct explanation for the assertion.

### Final Answer:
- The answer is **Option B**: Assertion is true, Reason is true, but Reason is not the correct explanation for Assertion.