Assertion: o-nitrophenol has higher boilling point than p-nitrophenol.
Reason: Intermolecular hydrogen bonding is present in p-nitrophenol and intrmolecular hydrogen bonding in o-nitrophenol.

Options

A. If both A and R are true and R is the correct explanation of A.
B. If both A and R are true but R is not the correct explanation of A.
C. If A is true but R is false
D. If A is false but R is true.

Explanation

To solve the given question, we need to analyze the assertion and reason provided, and then determine their validity.

### Step 1: Understand the Structures
- **Ortho-nitrophenol (o-nitrophenol)** has the nitro group (-NO2) and hydroxyl group (-OH) positioned on adjacent carbon atoms of the benzene ring.
- **Para-nitrophenol (p-nitrophenol)** has the nitro group and hydroxyl group positioned on opposite sides of the benzene ring.

### Step 2: Analyze Hydrogen Bonding
- **Ortho-nitrophenol** can form **intramolecular hydrogen bonding**. This means that the -OH group can form a hydrogen bond with the -NO2 group within the same molecule, which stabilizes the structure but does not contribute significantly to boiling point.
- **Para-nitrophenol** can form **intermolecular hydrogen bonding**. This means that the -OH group of one molecule can form hydrogen bonds with the -NO2 group of another molecule, leading to stronger interactions between molecules.

### Step 3: Compare Boiling Points
- Intermolecular hydrogen bonding is generally stronger than intramolecular hydrogen bonding. Therefore, para-nitrophenol, which exhibits intermolecular hydrogen bonding, will have a higher boiling point compared to ortho-nitrophenol, which primarily exhibits intramolecular hydrogen bonding.

### Step 4: Evaluate the Assertion and Reason
- **Assertion**: "o-nitrophenol has a higher boiling point than p-nitrophenol." This is **false** because para-nitrophenol has a higher boiling point due to stronger intermolecular hydrogen bonding.
- **Reason**: "Intermolecular hydrogen bonding is present in p-nitrophenol and intramolecular hydrogen bonding in o-nitrophenol." This is **true**.

### Conclusion
- The assertion is false, and the reason is true. Therefore, the correct answer is that the assertion is incorrect, but the reason is correct.

### Final Answer
- The assertion is false, and the reason is true.