Assertion(A): Langmuir adsorption is a single-layer phenomenon.
Reason(R): It is due to van der Waals forces.

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 analyze the given assertion and reason, we can break down the problem step by step.

### Step 1: Understand the Assertion
**Assertion (A): Langmuir adsorption is a single-layer phenomenon.**
- Langmuir adsorption theory states that gas molecules adsorb onto a solid surface to form a single molecular layer. This means that once a gas molecule occupies a site on the surface, no other molecule can occupy that same site, leading to a monolayer formation.

### Step 2: Understand the Reason
**Reason (R): It is due to van der Waals forces.**
- Van der Waals forces are weak intermolecular forces that can occur between molecules. However, in the context of Langmuir adsorption, the primary interactions involved are not just van der Waals forces but also include chemical bonding and the specific nature of the adsorbate and adsorbent.

### Step 3: Evaluate the Assertion and Reason
- The assertion is correct because Langmuir adsorption indeed describes a single-layer adsorption process.
- The reason is incorrect because while van der Waals forces may play a role in some adsorption processes, Langmuir adsorption does not rely solely on these forces. The adsorption is primarily due to the interaction of gas molecules with the surface of the adsorbent, which can include stronger interactions than van der Waals forces.

### Step 4: Conclusion
- Since the assertion is correct and the reason is incorrect, we conclude that:
- **Assertion (A) is true.**
- **Reason (R) is false.**

### Final Answer
The correct option is that the assertion is correct, but the reason is incorrect.

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