Ketones are generally less reactive than Aldehydes in nucleophilic addition reactions because

Explanation

This is attributed to the greater steric hindrance by the alkyl (or aryl) groups in ketones compared to one such group in aldehydes t the attacking nucleophile. Moreover, these groups also tend to increase the electron desnsity on the carbonyl carbon atom more in ketones in comparison to aldehydes. Ketones are therefore, less reactive than aldehydes in the nuclophilic addition reactions.