Which statement best describes the use of hydrogen as a fuel source? 

A)  Experimental cars have been running on hydrogen for years. 
B)  Metals cannot store and release hydrogen. 
C)  When burned, hydrogen produces air pollutants. 
D)  Fuel tanks containing metal-hydrogen compounds would tend to explode in an accident.

Experimental cars have been developed that are powered by hydrogen fuel cells, which convert hydrogen into electricity to power the vehicle. Hydrogen fuel cells have shown promise as a clean energy source for transportation.

Option B is false as some metals such as palladium can store and release hydrogen.

Option C is false as when burned, hydrogen produces only water vapor and no air pollutants.

Option D is false as fuel tanks containing metal-hydrogen compounds have been developed and are used safely in hydrogen fuel cell vehicles.