Assertion (A) o-nitrophenol is less soluble in water than the m and p-isomers.
Reason (R) m and p-nitrophenols exist as associated molecules.

Options

A. Assertion and reason both are correct and reason is correct explanation of assertion.
B. Assertion and reason both are wrong statements.
C. Assertion is correct statement but reason is wrong statement.
D. Assertion is wrong statement but reason is correct statement.

Explanation

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

**Assertion (A):** o-nitrophenol is less soluble in water than the m- and p-isomers.

**Reason (R):** m- and p-nitrophenols exist as associated molecules.

### Step-by-Step Solution:

1. **Understanding the Structures:**
- **o-Nitrophenol:** The nitro group (-NO2) is positioned ortho (adjacent) to the hydroxyl group (-OH).
- **m-Nitrophenol:** The nitro group is positioned meta (one carbon apart) from the hydroxyl group.
- **p-Nitrophenol:** The nitro group is positioned para (opposite) to the hydroxyl group.

2. **Analyzing Solubility:**
- **o-Nitrophenol:** In this isomer, the proximity of the nitro group to the hydroxyl group allows for **intramolecular hydrogen bonding**. This means that the -OH group can form a hydrogen bond with the -NO2 group within the same molecule, reducing its ability to interact with water molecules. As a result, o-nitrophenol is less soluble in water.
- **m- and p-Nitrophenols:** In contrast, these isomers do not have intramolecular hydrogen bonding. Instead, they can form **intermolecular hydrogen bonds** with water molecules, enhancing their solubility in water.

3. **Evaluating the Assertion:**
- The assertion is correct because o-nitrophenol is indeed less soluble in water compared to its m- and p-isomers due to intramolecular hydrogen bonding.

4. **Evaluating the Reason:**
- The reason states that m- and p-nitrophenols exist as associated molecules. This is somewhat misleading. While it is true that they can form hydrogen bonds with water, the term "associated molecules" is not the best explanation for their solubility. The key factor is the ability to form hydrogen bonds with water, not merely the existence of associated molecules.

5. **Conclusion:**
- Both the assertion and the reason are correct statements, but the reason does not correctly explain why the assertion is true. Therefore, the correct conclusion is that both the assertion and reason are correct, but the reason is not the correct explanation for the assertion.

### Final Answer:
- Assertion (A) is correct: o-nitrophenol is less soluble in water than m- and p-isomers.
- Reason (R) is also correct: m- and p-nitrophenols can form hydrogen bonds with water, but the term "associated molecules" is not an accurate explanation for their solubility.