Assertion : Acetone is less reactive towards nucleophilic addition than acetaldehyde.
Reason : The alkyl groups hinder the nucleophilic attack on carbonyl carbon atom.

Options

A. If both assertion and reason are correct and reason is correct explanation for assertion.
B. If both assertion and reason are correct and reason is not correct explanation for assertion.
C. If assertion is correct but reason is incorrect.
D. If assertion as well as reason are both incorrect.

Explanation

To solve the question regarding the reactivity of acetone and acetaldehyde towards nucleophilic addition, we will break down the assertion and reason step by step.

### Step-by-Step Solution:

1. **Understanding the Compounds**:
- Acetone (C3H6O) is a ketone with the structure CH3-C(=O)-CH3.
- Acetaldehyde (C2H4O) is an aldehyde with the structure CH3-C(=O)-H.

2. **Assertion Analysis**:
- The assertion states that "Acetone is less reactive towards nucleophilic addition than acetaldehyde."
- Aldehydes are generally more reactive than ketones in nucleophilic addition reactions. This is due to the presence of one alkyl group in aldehydes compared to two in ketones, which affects the reactivity.

3. **Reason Analysis**:
- The reason states that "The alkyl groups hinder the nucleophilic attack on the carbonyl carbon atom."
- In ketones like acetone, the presence of two bulky methyl groups creates steric hindrance, making it more difficult for nucleophiles to approach and attack the carbonyl carbon.

4. **Steric Effects**:
- The steric hindrance in acetone (due to two methyl groups) is greater than in acetaldehyde (which has only one methyl group and one hydrogen).
- This steric hindrance reduces the rate of nucleophilic attack on acetone compared to acetaldehyde.

5. **Electronic Effects**:
- Alkyl groups are electron-donating (through +I effect), which reduces the electrophilicity of the carbonyl carbon in ketones.
- In acetone, the two methyl groups decrease the positive character of the carbonyl carbon more than in acetaldehyde, making acetone less reactive.

6. **Conclusion**:
- Both the assertion and the reason are correct.
- The reason provided explains why the assertion is true: the presence of two alkyl groups in acetone hinders nucleophilic attack more than the single alkyl group in acetaldehyde.

### Final Answer:
Both the assertion and reason are correct, and the reason is the correct explanation for the assertion.