Why do hydrogen fuel cells have a low environmental impact?

• A. They produce carbon dioxide during operation.
• B. They release no carbon dioxide when hydrogen is produced by water.
• C. They require no energy input at all.
• D. They emit methane during operation.

Answer: (B)

Fuel cells generate electricity by turning hydrogen and oxygen into water and heat, without burning fuel. That means no combustion emissions, so nothing like carbon dioxide or methane is produced during operation. The environmental advantage is strongest when the hydrogen itself is produced using clean electricity (for example, splitting water with renewable energy), because then the whole cycle adds little to no CO2. The other ideas don’t fit because the cell’s operation doesn’t emit CO2 or methane, and the requirement of energy input is about producing hydrogen or running the system—not about what happens in the fuel cell’s chemical reaction itself.