State the advantages of obtaining biogas from animal dung and bio-wastes.

11 Why is charcoal considered a better fuel than wood? What are the disadvantages of converting wood into charcoal? 12 Describe the steps involved in obtaining biogas and explain what is meant by anaerobic decomposition. 14 Why are fossils fuels classified as non-renewable sources of energy? What steps should be taken to conserve these sources? 15 The heat produced on complete combustion of 10 g of a fuel could raise the temperature of 2 kg of water from 20° C to 70° C. Calculate the calorific value of the fuel, if the specific heat capacity of water was 4.2 J/g ° C. Assume that the heat taken by the container is negligible.