A : Aromatic aldehydes are less reactive than aliphatic aldehyde towards nucleophilic substitution reaction.
R : In case of aromatic aldehyde,+R effect of phenyl ring 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 aromatic and aliphatic aldehydes, their reactivity towards nucleophilic substitution reactions, and the influence of resonance.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "aromatic aldehydes are less reactive than aliphatic aldehydes towards nucleophilic substitution reactions."
- This means that when a nucleophile (a species that donates an electron pair) approaches the carbonyl carbon of an aldehyde, aromatic aldehydes do not react as readily as their aliphatic counterparts.

2. **Understanding the Reason**:
- The reason given is that "in case of aromatic aldehyde, the +R effect (resonance effect) of the phenyl ring is present."
- The +R effect refers to the electron-donating resonance effect that occurs when a substituent (like a phenyl ring) can donate electron density to the rest of the molecule.

3. **Analyzing Aromatic Aldehydes**:
- In aromatic aldehydes, the carbonyl carbon (C=O) is part of a system that can delocalize electrons due to the presence of the benzene ring.
- The resonance structure allows the lone pair of electrons on the oxygen to be shared with the π system of the benzene ring, which decreases the positive character of the carbonyl carbon.

4. **Analyzing Aliphatic Aldehydes**:
- In contrast, aliphatic aldehydes do not have such resonance stabilization. The carbonyl carbon retains a higher positive charge density because there are no electron-donating groups to stabilize it.
- This higher positive charge density makes the carbonyl carbon more susceptible to attack by nucleophiles.

5. **Conclusion**:
- Since aromatic aldehydes have a decreased positive charge density due to resonance, they are less reactive towards nucleophilic substitution compared to aliphatic aldehydes.
- Therefore, both the assertion and the reason are correct, and the reason correctly explains the assertion.

### Final Answer:
Both the assertion (A) and the reason (R) are correct, and the reason is a correct explanation of the assertion.