What is a key benefit of hydrogen fuel cells?

• A. They emit large quantities of greenhouse gases
• B. They require frequent replacement of catalysts
• C. Only by-products are water/steam/heat, with minimal emissions
• D. They cannot be scaled to different sizes

Answer: (C)

The main idea is that hydrogen fuel cells generate electricity with very low emissions during operation because the chemical reaction between hydrogen and oxygen produces electrical energy and mainly water (with some heat) as the by-products. This means the device runs cleanly, producing minimal greenhouse gases at use, which is the strongest advantage for environmental and air-quality reasons. Hydrogen fuel cells can also be scaled to different sizes—from small units for vehicles to large installations—so size flexibility is a real strength, not a limitation. The other statements describe drawbacks or false limits (like frequent catalyst replacement or being unable to scale), which aren’t defining benefits of the technology.