Hydrogen-Oxygen Fuel Cell Reaction

Steps:

• Identify the electrochemical reaction: 2H₂ + O₂ → 2H₂O.
• Note the single product: water (liquid or vapor).
• Compare to options: A states one product, matching the reaction.
• Eliminate others: B involves combustion, C reverses energy flow, D contradicts efficiency facts.

Why A is correct:

• The half-cell reactions combine to form only H₂O, per the balanced equation 2H₂ + O₂ → 2H₂O.

Why the others are wrong:

• B: Fuel cells produce electricity via redox reactions, not combustion in air.
• C: Fuel cells generate electrical energy from chemical input, not consume it.
• D: Fuel cells achieve 40-60% efficiency, higher than petrol engines' 20-30%.

Final answer: A