Which species acts as the reducing agent in the reaction between hydrazine and chlorate in basic solution?

• A. N2H4
• B. ClO3−
• C. NO
• D. Cl−

Answer: (A)

In a redox process, the reducing agent is the substance that loses electrons (is oxidized). Hydrazine does just that in basic solution: it is oxidized to nitrogen gas, releasing electrons that chlorate can gain as it is reduced. The oxidation half-reaction in base is N2H4 + 4 OH− → N2 + 4 H2O + 4 e−, showing hydrazine donating electrons. Chlorate is reduced, typically to chloride, by accepting those electrons (for example, ClO3− + 6 H2O + 5 e− → Cl− + 12 OH−). So hydrazine acts as the reducing agent because it is the species being oxidized.