Ketones are less reactive in nucleophilic substitution because:

Explanation

Ketones are indeed less reactive in nucleophilic substitution reactions compared to aldehydes. One of the reasons for this is that ketones have an electron-donating environment around the carbon-oxygen double bond. This electron-donating effect makes it harder for nucleophiles to attack the carbon atom in the ketone molecule. In contrast, aldehydes have a more electron-withdrawing environment, which makes them more reactive towards nucleophilic substitution. This difference in reactivity is due to the presence of the additional alkyl group in ketones, which stabilizes the molecule and reduces its reactivity.