The correct answer is (a) Hydrogen.
Hydrogen is a clean-burning fuel that produces no emissions. It is also the most abundant element in the universe, making it a sustainable option for the future.
Power alcohol is a fuel made from ethanol, which is a type of alcohol produced from plant materials. Ethanol is a renewable fuel that produces fewer emissions than gasoline. However, it is not as clean-burning as hydrogen and can contribute to air pollution.
Petrol is a fossil fuel that produces emissions that contribute to climate change and air pollution. It is also a non-renewable resource that is becoming increasingly scarce.
Compressed natural gas (CNG) is a fossil fuel that produces fewer emissions than gasoline. However, it is still a non-renewable resource and contributes to climate change.
In conclusion, hydrogen is the best option for a fuel that produces the least environmental pollution. It is a clean-burning, sustainable fuel that is abundant in the universe.