Which of the structures shown is more reactive than the ketone shown towards nucleophilic addition of cyanide?

Methanal has two hydrogens on the carbonyl carbon, so it is the least hindered and the most electrophilic of the group. The more hindered diisopropyl ketone, the conjugated and less electrophilic acetophenone and the ester (stabilised by resonance of the OMe lone pair) are all less reactive than propanone.