Correct Option (c):
Hydrogen fuel cells generate electricity through an electrochemical reaction between hydrogen (H₂) and oxygen (O₂) from the air. The primary and only significant byproduct of this reaction is water (H₂O), which is released as exhaust, typically in the form of water vapor or liquid droplets. This process is considered environmentally clean as it produces no greenhouse gases or other air pollutants at the point of operation.
Incorrect Options:
- (a) NH₃ (Ammonia): Ammonia is not produced as an exhaust product in standard hydrogen fuel cell operations. Its chemical composition and formation mechanism are unrelated to the electrochemical conversion of hydrogen and oxygen.
- (b) CH₄ (Methane): Methane is a hydrocarbon fuel and not a product of a hydrogen fuel cell. While methane can be used as a source to produce hydrogen through reforming processes, it is not an emission from a hydrogen fuel cell vehicle itself.
- (d) H₂O₂ (Hydrogen peroxide): Hydrogen peroxide is a reactive chemical compound and not a stable or intended exhaust product of a hydrogen fuel cell. Its formation in significant quantities is not part of the designed fuel cell reaction mechanism.