Read the Passage carefully and answer the questions.

The carbonyl group of aldehydes and ketones is highly polar. The positively charged carbon is readily attacked by electron-rich nucleophile and the negatively charged oxygen atom is attacked by an electro-deficient electrophile. Aldehydes and ketones undergo nucleophilic addition reactions in the presence of acid or a base. The mechanism involves attack of a nucleophile on the electron deficient carbonyl carbon to form a tetrahedral intermediate. A new bond is formed between the carbon and oxygen. Protonation of the anion furnished by the reaction medium yields a neutral addition product. The addition product is same whether the reaction is catalyzed by acid or a base. For example in the presence of base aldehydes and ketones react with hydrogen cyanide to form cyanohydrin.

The source of nucleophile in the base catalyzed cyanohydrin formation is

KCN

The correct answer is Option (2) → KCN **

In base-catalyzed cyanohydrin formation, the nucleophile is the cyanide ion (CN⁻), which attacks the electrophilic carbonyl carbon.

• KCN or NaCN provides the CN⁻ ion in solution.
• HCN is the source of cyanide under acidic or neutral conditions, but in base-catalyzed reactions, the cyanide ion comes from the salt.