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I am not 100% sure that this is true but this was given in the JEE Main 2020 (03 Sep Shift 2).

Benzaldehyde has resonance and propanone has just +I effect why is then benzaldehyde more reactive in nucleophilic addition?

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The carbonyl carbon exhibits reactivity towards nucleophilic addition reactions due to its partial positive charge resulting from oxygen. enter image description here

Benzaldehyde's heightened reactivity, compared to propanone, can be attributed to the absence of electron-donating methyl groups. In propanone, two methyl groups act as electron donors, whereas benzaldehyde features an sp2 carbon attached to the carbonyl carbon, which, being more electronegative than sp3 carbons, does not exert a +I effect like methyl carbons.

Additionally, steric hindrance is induced by the presence of two methyl groups in propanone.

While benzene does contribute to reducing the positive charge through resonance, it is imperative to consider the impact of other influencing factors. enter image description here

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