A : p - nitrophenol has high `pK_(a)` in comparison to o-nitrophenol
R : In o-nitrophenol , intermolecular H-bonding is present

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false , then mark (3)
D. If both Assertion and Reason are false statements , then mark (4)

Answer

To analyze the assertion and reason provided in the question, we will break down the concepts of pKa, acidity, and hydrogen bonding in ortho- and para-nitrophenol.

### Step-by-Step Solution:

1. **Understanding pKa and Acidity**:
- The pKa value is a measure of the acidity of a compound. A higher pKa value indicates a weaker acid, while a lower pKa value indicates a stronger acid.
- Therefore, if para-nitrophenol has a higher pKa value than ortho-nitrophenol, it means that para-nitrophenol is a weaker acid compared to ortho-nitrophenol.

2. **Structure of Ortho- and Para-Nitrophenol**:
- Para-nitrophenol has the nitro group (NO2) positioned at the para position relative to the hydroxyl group (OH).
- Ortho-nitrophenol has the nitro group positioned at the ortho position relative to the hydroxyl group.

3. **Intermolecular Hydrogen Bonding in Ortho-Nitrophenol**:
- In ortho-nitrophenol, the proximity of the hydroxyl group and the nitro group allows for intramolecular hydrogen bonding, which stabilizes the molecule.
- This intramolecular hydrogen bonding reduces the availability of the hydrogen atom from the hydroxyl group to dissociate as a proton (H+), thus increasing the acidity of ortho-nitrophenol compared to para-nitrophenol.

4. **Conclusion on Assertion and Reason**:
- The assertion (A) that para-nitrophenol has a higher pKa than ortho-nitrophenol is true.
- The reason (R) that intermolecular hydrogen bonding is present in ortho-nitrophenol is misleading. It should be noted that it is intramolecular hydrogen bonding that affects the acidity.
- Therefore, while both the assertion and reason are true, the reason does not correctly explain the assertion.

### Final Answer:
- Assertion (A) is true.
- Reason (R) is true but does not explain (A) correctly.