11. Answer in detail III

 

Fuels are classified into three different types based on their physical state. They are

 

a. Wood and coal. These fuels are easy to carry and store. The cost of production is also very low: Solid fuelsLiquid fuelsGaseous fuels

b. The majority of these fuels come from the leftovers of dead plants and animals: Gaseous fuelsLiquid fuelsSolid fuels

 

These fuels burn with more energy without ash.

c. Coal gas, oil gas, producer gas and hydrogen gas. These fuels are easy to transport through pipes and do not pollute the environment: Solid fuelsLiquid fuelsGaseous fuels