Concept:Carbonyl compounds (aldehydes and ketones) undergo reactions initiated by nucleophiles because the carbonyl carbon is electron-deficient (partially positive).
Solution:- In the reaction with HCN, the attacking species is the strong nucleophile \( CN^- \).
- The \( CN^- \) attacks the electrophilic carbonyl carbon of ethanal, adding itself to the molecule.
- The \( \pi \) bond breaks and the oxygen accepts a proton, creating a single tetrahedral product. Because two molecules merge into one without any byproducts leaving, it is strictly an addition reaction.
- Thus, it is a Nucleophilic Addition reaction.
Why other options are incorrect:Substitution implies replacing an atom, but here no atoms are lost. Electrophilic addition is characteristic of alkenes where the initial attack is by an electrophile (like \( H^+ \)), not a nucleophile.
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