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

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 not 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 question, we need to analyze both the assertion and the reason provided.

### Step 1: Understand 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 volume occupied by gas molecules and the intermolecular forces between them. It is given by:

\[ \left(P + \frac{a n^2}{V^2}\right)(V - nb) = nRT \]

Here, \(P\) is the pressure, \(V\) is the volume, \(n\) is the number of moles, \(R\) is the gas constant, and \(T\) is the temperature. The terms \(a\) and \(b\) are constants specific to each gas.

- The van der Waals equation is specifically designed to describe the behavior of real gases, which do not behave ideally under all conditions. Therefore, the assertion is **correct**.

### Step 2: Understand the Reason
The reason states that "ideal gases obey the equation \(PV = nRT\)."

- The equation \(PV = nRT\) is known as the ideal gas law, which describes the behavior of ideal gases. Ideal gases are hypothetical gases that perfectly follow this equation under all conditions of temperature and pressure.

- Since ideal gases do not take into account the volume of gas particles or intermolecular forces, they are described by this equation without any corrections. Therefore, the reason is also **correct**.

### Step 3: Determine the Relationship Between Assertion and Reason
Now, we need to determine if the reason correctly explains the assertion.

- The assertion is about the applicability of the van der Waals equation to non-ideal gases, while the reason discusses the behavior of ideal gases under the ideal gas law.

- The reason provides context for why the van der Waals equation is necessary (because ideal gases follow a different law), thus it can be considered a correct explanation for the assertion.

### Conclusion
Both the assertion and the reason are correct, and the reason is a correct explanation for the assertion.

### Final Answer
- **Assertion**: Correct
- **Reason**: Correct
- **Explanation**: The reason correctly explains why the van der Waals equation is applicable only to non-ideal gases.

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