KEAM 2010 Physics and Chemistry Paper

The carbonyl compounds must contain an α -hydrogen atom to undergo aldol condensation. Thus, propanal and ethanal are the aldehydes that can undergo aldol condensation.
However, methanal though does not contain α -hydrogen atom yet undergoes cross aldol condensation in the presence of limewater.
Thus, aldehydes that do not undergo aldol condensation are trichloroethanal, benzaldehyde and methanal.