Option 1..is correct NaHSO3..
the rkn is steric sensitive since attacking nucleophile is a bulky group so all carbonyl compounds cannot show the rkn so the rkn is possible in
1)all aldehydes including benzaldehyde
2)those methyl ketones in which 2nd group is alkyl not aryl

The reagent used for the separation of acetaldehyde from acetophenone is NaHSO3 (sodium bisulfite). This reagent is commonly used in organic chemistry for the selective reduction of aldehydes. The reaction between NaHSO3 and aldehydes is known as the bisulfite addition reaction.

Explanation:

1. Reagent: NaHSO3
- Sodium bisulfite is a white crystalline solid that is soluble in water.
- It is a mild reducing agent and reacts selectively with aldehydes.
- The reaction between NaHSO3 and aldehydes forms a bisulfite adduct, which is highly stable and easily separated from other compounds.

2. Purpose: Separation of acetaldehyde from acetophenone
- Acetaldehyde and acetophenone are both carbonyl compounds, but they have different reactivity towards NaHSO3.
- Acetaldehyde reacts readily with NaHSO3 to form a bisulfite adduct, while acetophenone does not undergo this reaction.
- By treating the mixture of acetaldehyde and acetophenone with NaHSO3, acetaldehyde can be selectively converted into its bisulfite adduct, allowing for its separation from acetophenone.

3. Reaction mechanism:
- The reaction between acetaldehyde and NaHSO3 proceeds via nucleophilic addition.
- NaHSO3 acts as a nucleophile, attacking the carbonyl carbon of acetaldehyde.
- This results in the formation of a hemiacetal intermediate.
- The intermediate then reacts with another molecule of NaHSO3 to form the bisulfite adduct.
- In contrast, acetophenone does not have a reactive carbonyl group that can undergo nucleophilic addition with NaHSO3.

4. Separation process:
- After the reaction with NaHSO3, the bisulfite adduct of acetaldehyde can be easily separated from the reaction mixture.
- The adduct has different physical properties compared to acetophenone, such as solubility and stability.
- It can be isolated by techniques like filtration or extraction.
- The adduct can then be converted back to acetaldehyde by treatment with a suitable reagent, such as NaOH or acid.

In summary, the reagent NaHSO3 is used for the separation of acetaldehyde from acetophenone due to its selective reaction with aldehydes. The reaction forms a stable bisulfite adduct that can be easily separated from other compounds. This separation process allows for the isolation of acetaldehyde from a mixture containing acetophenone.