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📌 The Question:
Which one of the following is the exhaust pipe emission from Fuel Cell Electric Vehicles (FCEVs) powered by hydrogen?

(a) Hydrogen peroxide
(b) Hydronium
(c) Oxygen
(d) Water vapour

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✅ Correct Answer: (d) Water vapour

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⚡ Lightning Classroom Explanation:

Fuel Cell Electric Vehicles (FCEVs) operate by combining hydrogen (H₂) stored in the vehicle with oxygen (O₂) from the air inside a fuel cell stack.

🔬 Core Reaction inside a fuel cell:
Hydrogen + Oxygen → Electricity + Heat + Water

• The electricity powers the motor
• Heat is dissipated
• Water vapour is released through the exhaust pipe

There is no combustion, no CO₂, no NOₓ, no particulate matter.

Hence, the only tailpipe emission is water vapour.

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🧠 Curiosity Raiser:
👉 A hydrogen car cleans the air it uses, but its true climate impact depends on how hydrogen itself is produced.

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📚 Enrich Notes (UPSC Edge):

• FCEVs ≠ Battery EVs (they generate electricity onboard)
• Hydrogen used is often grey/blue/green depending on source
• Green hydrogen + FCEVs = true zero-emission mobility

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🕊️ IAS Monk Whisper:
“When energy is born from hydrogen, the exhaust carries only a trace of rain.”