• Coal-  Coal has been the primary source of energy since the advent of industrialization. It is mainly composed of carbon, however also content hydrogen,oxygen and varying amounts of nitrogen, sulphur and other elements in small quantities. It is developed from decomposition of vegetable matters, trees, plats which falls and buried under heavy pressure, heat and movement of earth crust.                          Coal has low calorific value and its transportation cost is more. Further, it is highly pollutants and produces CO2, CO, H2S, SO2 on combustion. That is why world is now switching over to oil as a major source of energy  because of its simpler and cleaner to obtain useful energy from oil.