Arrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions. Ethanal (I), Propanal (II), Propanone (III), Butanone (IV)

The order of the reactivity towards the Nucleophilic addition reaction can be decided on the factor of electron density on the carbonyl compound. So, as the alkyl group increases the +I-effect increases and the electron density on the carbonyl group increases, this makes difficult for the nucleophile to attack. So, the order of reactivity will be Ethanal > Propanal > Propanone > Butanone.