Assertion: Benzaldehyde is more reactive than ethanal towards nucleophilic attact.
Reason : The overall effect of- `l` and `+R` effect of phenyl group decrease the electron density on the carbon atom of `gtC = O` group in benzaldehyde.

Options

A. if both assertion and reason are true and reason is thr correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reson are false.

Explanation

To solve the assertion and reason question, we need to analyze both statements carefully.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- **Assertion**: Benzaldehyde is more reactive than ethanal towards nucleophilic attack.
- **Analysis**: Both benzaldehyde (C6H5CHO) and ethanal (CH3CHO) contain a carbonyl group (C=O), which is the site of nucleophilic attack. The reactivity towards nucleophilic attack depends on the electron density on the carbon atom of the carbonyl group.

2. **Comparing the Structures**:
- Benzaldehyde has a phenyl group (C6H5) attached to the carbonyl carbon.
- Ethanal has a methyl group (CH3) attached to the carbonyl carbon.
- The presence of different substituents (phenyl in benzaldehyde and methyl in ethanal) influences the electron density on the carbonyl carbon.

3. **Analyzing Electron Effects**:
- In benzaldehyde, the phenyl group exhibits:
- **-I (Inductive Effect)**: The phenyl group pulls electron density away from the carbonyl carbon, increasing its positive character (δ+).
- **+R (Resonance Effect)**: The phenyl group can also donate electron density through resonance, which can decrease the positive character of the carbonyl carbon.
- In ethanal, the methyl group exhibits:
- **+I (Inductive Effect)**: The methyl group donates electron density, which decreases the positive character of the carbonyl carbon.
- **+H (Hyperconjugation)**: The methyl group can stabilize the carbonyl carbon through hyperconjugation, further decreasing its positive character.

4. **Determining Reactivity**:
- The overall effect of the phenyl group in benzaldehyde results in a higher positive charge density on the carbonyl carbon compared to ethanal.
- Therefore, benzaldehyde is indeed more reactive than ethanal towards nucleophilic attack.

5. **Understanding the Reason**:
- **Reason**: The overall effect of -I and +R effect of the phenyl group decreases the electron density on the carbon atom of the C=O group in benzaldehyde.
- **Analysis**: This statement is true as the -I effect increases the positive charge density on the carbonyl carbon, making it more susceptible to nucleophilic attack.

6. **Conclusion**:
- Both the assertion and the reason are true.
- The reason correctly explains the assertion.

### Final Answer:
The correct answer is option A: Both assertion and reason are true, and the reason correctly explains the assertion.