Detailed Explanation:

Correct Answer: ✅ Water Vapour (Option D)

Fuel Cell Electric Vehicles (FCEVs) use hydrogen as fuel. Inside the fuel cell, hydrogen reacts with oxygen from the air to generate electricity that powers the vehicle.

The by-products of this reaction are water (H₂O) and heat. Therefore, the only exhaust emission released from the vehicle's tailpipe is water vapour, making FCEVs a clean-energy transportation technology.

❌ Hydrogen Peroxide: Not produced as a normal exhaust product in fuel cells.

❌ Hydronium (H₃O⁺): Exists in aqueous solutions and is not emitted from vehicles.

❌ Oxygen: Oxygen is consumed in the reaction, not emitted.

✅ Water Vapour: The primary and only exhaust emission from hydrogen fuel cell vehicles.

Short Notes: Fuel Cell Electric Vehicles (FCEVs)

• FCEVs use hydrogen (H₂) as fuel to generate electricity.

• Electricity is produced through an electrochemical reaction, not combustion.

• Main reaction: Hydrogen + Oxygen → Electricity + Water + Heat.

• The exhaust emission is only water vapour (H₂O).

• Fuel cells are considered zero tailpipe emission technology.

• Hydrogen is stored in high-pressure tanks inside the vehicle.

• Examples include the Toyota Mirai and Hyundai Nexo.

• FCEVs offer fast refuelling and longer driving ranges compared to many battery EVs.