Arrange in decreasing order of reactivity towards nucleophilic addition: CH₃CHO, CH₃COCH₃, C₆H₅COCH₃.
Aldehydes are more reactive than ketones: CH₃CHO (aldehyde) > CH₃COCH₃ (simple ketone) > C₆H₅COCH₃ (aromatic ketone, steric hindrance).
Ref: NCERT Class 12 Chemistry > Chapter 12: Aldehydes, Ketones and Carboxylic Acids > Topic: Physical Properties and Nucleophilic Addition Reactions