UPSC Prelims 2010 Q36: Science & Technology – Energy & Environment
Hydrogen fuel - cell vehicles produce one of the following as “exhaust”.
- (a) NH₃
- (b) CH₄
- (c) H₂O
- (d) H₂O₂
Answer: (c) H₂O
Explanation
What hydrogen fuel-cell vehicles emit as "exhaust"
Hydrogen fuel cells generate electricity through a clean chemical reaction, producing a notably benign byproduct.
| Option | Verdict | Reason |
|---|---|---|
| (a) NH₃ (Ammonia) | Incorrect | Ammonia is not the fuel-cell reaction product |
| (b) CH₄ (Methane) | Incorrect | Methane is a hydrocarbon fuel, not a hydrogen fuel-cell exhaust product |
| (c) H₂O (Water) | Correct | Hydrogen fuel cells combine hydrogen and oxygen electrochemically, producing electricity, heat, and water vapour as the only exhaust |
| (d) H₂O₂ (Hydrogen peroxide) | Incorrect | Hydrogen peroxide is not the standard fuel-cell byproduct |
Hydrogen fuel cell basics:
| Point | Detail |
|---|---|
| Reaction | H₂ + O₂ → H₂O + electricity + heat |
| Exhaust | Water (H₂O) only |
| Environmental appeal | Zero direct carbon emissions at point of use |
Answer: (c) H₂O.
Why each option is right or wrong
- (a) Incorrect. Ammonia is unrelated to the hydrogen-oxygen fuel-cell reaction.
- (b) Incorrect. Methane is a hydrocarbon fuel, not a fuel-cell exhaust product.
- (c) CORRECT. The fuel-cell reaction of hydrogen and oxygen produces water (H₂O) as its exhaust.
- (d) Incorrect. Hydrogen peroxide is not the standard byproduct of this clean electrochemical reaction.
Key point
Hydrogen fuel-cell vehicles combine hydrogen and oxygen to produce electricity, with WATER (H₂O) as the only exhaust byproduct — making them essentially zero direct-emission vehicles.
Remember
Hydrogen fuel-cell vehicles exhaust only water (H₂O) as a byproduct of generating electricity.
Common mistakes
- Confusing the clean water byproduct of fuel cells with pollutant gases from combustion engines.
- Mixing up hydrogen peroxide with plain water as the fuel-cell exhaust.
- Not understanding the basic H₂ + O₂ → H₂O electrochemical reaction.
Exam tip
Hydrogen fuel cell = H₂ + O₂ → H₂O + electricity. Water is the only exhaust, making it a near-zero-emission technology.
Sources
- Ministry of New and Renewable Energy, Government of India — National Hydrogen Energy Road Map (2006)
- NCERT Class XII Chemistry — Electrochemistry (fuel cells)