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.

Which of the following compounds will undergo nucleophilic addition readily?

Formaldehyde

The correct answer is Option (1) → Formaldehyde **

Nucleophilic addition to a carbonyl compound is favored when:

• Steric hindrance is minimum
• +I / electron-donating effects are minimum
• Carbonyl carbon is most electrophilic

Comparison of options:

• Formaldehyde (HCHO) → no alkyl groups, least steric hindrance, highest electrophilicity
• Acetaldehyde (CH₃CHO) → one alkyl group
• Benzaldehyde (C₆H₅CHO) → resonance donation from phenyl ring reduces electrophilicity
• Butanone (CH₃COC₂H₅) → ketone + steric hindrance

Hence Formaldehyde is the correct answer