Less Reactivity of Ketones compared to Aldehydes
Ketones are less reactive than aldehydes towards nucleophilic addition due to structural and electronic factors.

Electronic Factors
• The presence of an additional alkyl group attached to the carbonyl carbon in ketones decreases the electrophilicity of the carbon atom compared to aldehydes which have a hydrogen atom.
• The electron-donating alkyl groups in ketones stabilize the partially positive carbonyl carbon, reducing its reactivity towards nucleophilic attack.

Steric Factors
• The presence of two alkyl groups in ketones creates steric hindrance around the carbonyl carbon, making it more difficult for nucleophiles to approach and react with the carbon atom compared to aldehydes which have only one alkyl group.
• This steric hindrance reduces the likelihood of nucleophilic addition reactions in ketones.

Overall
In conclusion, the combination of electronic and steric factors in ketones makes them less reactive towards nucleophilic addition reactions compared to aldehydes. The presence of alkyl groups in ketones stabilizes the carbonyl carbon and creates steric hindrance, both contributing to the decreased reactivity of ketones in nucleophilic addition reactions.