Reaction of a carbonyl compound with one of the following reagents involves nucleophilic addition followed by the elimination of water. The reagent is:

The reaction of aldehydes and ketones with ammonia derivatives ($H_2N-Z$) is a characteristic nucleophilic addition-elimination reaction.

1. Mechanism: The nitrogen atom of the nucleophile attacks the carbonyl carbon (nucleophilic addition) to form a tetrahedral intermediate. This intermediate then loses a molecule of water (elimination) to form a compound with a $>C=N-Z$ double bond.
2. Hydrazine: Hydrazine ($NH_2NH_2$) reacts with carbonyl compounds in a feebly acidic medium to eliminate water and form hydrazones. $>C=O + H_2N-NH_2 \xrightarrow{H^+} >C=N-NH_2 + H_2O$
3. Other Options:

• Grignard reagent: Undergoes nucleophilic addition to form an alkoxide, which yields an alcohol upon hydrolysis (no water elimination in the addition step).
• Hydrocyanic acid (HCN): Undergoes nucleophilic addition to form cyanohydrins (no water elimination).
• Sodium hydrogen sulphite: Undergoes nucleophilic addition to form bisulphite addition products (no water elimination).