why ethanal is more reactive towards nucleophilic addition reactions than propanone??

Oxygen is far more electronegative than carbon and so has a strong ... up a
carbon-oxygen double bond is even more easily pulled towards the oxygen.

Hence in ethalnal -OH group is present and the nucleophile easily attaches on oxygen than -CHO in propanone.

but there''s no -OH group in ethanal , a -CHO group is there....

because aldehyde is more reactive than ketones................

Better electrophile has greater reactivity towards nucleophilic addition reaction. As ethanal is better electrophile than propanone

it is more reactive towards nucleophilic addition reaction.

Propanone is a weak electrophile than ethanal because it has two methyl groups which contribute to +I effect