a)Hydrogen is not used as a common fuel because when it is lighted, it burns with an explosion and it is very difficult to store and transport hydrogen.
b) Fuel cells are being developed that can store energy produced by burning hydrogen. Development of materials that can absorb hydrogen and then release it at a steady rate.

The glass windows have the property to pass through it only radiations which have wavelength near to the visible light or shorter wavelength. It does not allow infrared radiations of higher wavelength. Since the sun sends infrared radiations of lower wavelength, these pass through the glass windows, get trapped inside the car as heat. The heat or infrared radiations of higher wavelength do not pass out the car and thus heat gets trapped in the car for longer time.

Yes. It is true that energy can neither be created nor destroyed and one form of energy is converted into another form. But the energy in the usable form is dissipated to the surrounding in the less usable form.

Acid rains are most likely expected in industrial areas where there is emission of oxides of nitrogen and sulphur.

For this purpose ocean thermal energy conversion (OTEC) power plants are used. To use this plant a difference of 200C or more between the temperature of surface waters and water at depths of 1000 metres is required. In one of Ocean Thermal Energy Conversion system, the warm surface water is used to boil low boiling liquid like Ammonia or a chlorofluorocarbon. The vapors of the liquid are then sent to move the turbines of generator. The cold water from the depths is used to cool the vapor escaped from the turbines and converted into liquid to be used again.