Cyanohydrin Formation Mechanism Steps:

• Acetone (CH3COCH3) is a ketone that undergoes nucleophilic addition with HCN.
• CN⁻ attacks the electrophilic carbonyl carbon, forming a tetrahedral alkoxide intermediate.
• The alkoxide abstracts a proton from HCN, yielding the cyanohydrin CH3C(OH)(CN)CH3 and regenerating CN⁻.
• This shows CN⁻ acts catalytically, as it is regenerated and not net consumed.

Why D is correct:

• Cyanide ion (CN⁻) catalyzes the reaction by serving as the nucleophile in addition and being regenerated via proton transfer from HCN, per the standard base-catalyzed mechanism.

Why the others are wrong:

• A: The product CH3C(OH)(CN)CH3 has two identical CH3 groups attached to the central carbon, so no chiral center.
• B: The reaction is nucleophilic addition (CN⁻ attacks carbonyl), not electrophilic.
• C: While the intermediate contains -CN, the statement's wording implies the product forms an intermediate with -CN, which is unclear and not accurate.

Final answer: D