Butanone is less reactive than propanal towards nucleophilic addition reaction because:

more \(+I\) effect found in butanone

The correct answer is option 1. more \(+I\) effect found in butanone.

The correct answer is option 1. more \(+I\) effect found in butanone it implies that butanone has more electron-donating groups or substituents than propanal, leading to an increase in electron density around the carbonyl carbon atom in butanone. This increased electron density would make the carbonyl carbon less electrophilic, resulting in decreased reactivity towards nucleophilic addition reactions compared to propanal.

In butanone (\(CH_3-CO-CH_2-CH_3\)), the two methyl (\(CH_3\)) groups attached to the carbonyl carbon can exert a \(+I\) effect, donating electron density towards the carbonyl carbon. This donation of electrons by the methyl groups would indeed decrease the electrophilicity of the carbonyl carbon in butanone.

Meanwhile, in propanal (\(CH_3-CH_2-CHO\)), there is only one methyl group attached to the carbonyl carbon. Therefore, the \(+I\) effect from the methyl group in propanal is less pronounced compared to the two methyl groups in butanone.

Thus, the increased \(+I\) effect from the two methyl groups in butanone compared to the single methyl group in propanal would indeed lead to a decrease in the electrophilicity of the carbonyl carbon in butanone, making butanone less reactive towards nucleophilic addition reactions.

Therefore, option 1. more \(+I\) effect found in butanone is the correct answer.