Arrange the following compounds in increasing order of their reactivity towards nucleophilic addition reaction:

(A) Ethanal
(B) Propanal
(C) Propanone
(D) Butanone

Choose the correct answer from the options given below:

(D), (C), (B), (A)

The correct answer is Option (1) → (D), (C), (B), (A)

Aldehydes are more reactive than ketones in nucleophilic addition reactions due to two main factors: electronic and steric effects. Electronically, the carbonyl carbon in an aldehyde is more positive because it is bonded to only one electron-donating alkyl group, compared to the two alkyl groups in a ketone. Sterically, the two alkyl groups on a ketone create more hindrance, making it more difficult for a nucleophile to attack the carbonyl carbon. 

Increasing Order (least reactive → most reactive):

Butanone (more hindered ketone) (D) < Propanone (ketone) (C) < Propanal (B) < Ethanal (A) (less hindered aldehyde)