Question

Benzaldehyde is less reactive than propanal in nucleophylic additional reaction

Answer 1

Polarity of carbonyl group in benzaldehyde is reduced due to resonance,, making it less reactive in nucleophilic addition reactions. but there is no such resonance effect in propanal and therefore,  the polarity of carbonyl group in propanal is more than in benzaldehyde. So,  propanal is more reactive than benzaldehyde.