Observe the diagram given below and answer the questions :[Diagram: the biofuel production cycle (textbook fig. 7.8): plants and crops take in CO2 and sunlight, crop and animal waste is processed into fuel, the fuel is used by vehicles and machines,…

Answer: (a) Biofuel. (b) Solid fuels: coal (also dung cakes, crop residue/wood); liquid fuels: alcohol (ethanol) and vegetable oils.

(a) The diagram shows the cycle of biofuel production: plants (forest/crops) use solar energy and CO₂; the biomass is harvested, its cellulose is converted into sugar, and liquid fuel is produced by fermentation in the factory. This biofuel runs cars, trucks and aeroplanes, and the CO₂ released is taken up again by plants. (Textbook figure 7.8 ‘Biofuel production’.)

(b) As per the textbook, biofuels are available in solid form (coal, dung, crop residue), liquid form (vegetable oils, alcohol) and gaseous form (gobar gas, coal gas).

Solid fuels: coal, dung cakes (crop residue). Liquid fuels: ethanol (alcohol), vegetable oils. (Petrol and diesel are also liquid fuels, but they are fossil fuels.)