1. (A) gives brisk effervescence with Na2CO3 means it must be a carboxylic acid. So (A) must be CH3COOH Acetic acid.
2. Acetic acid reacts with thionyl chloride to give acetyl chloride CH3COCI as (B)
3. Acetyl chloride reacts with Pd/BaSO4 , it undergoes Rosenmund’s reduction to give acetaldehyde as (C)
4. When acetaldehyde is warmed with dilute NaOH, it undergoes aldol condensation to