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(i)┬а Conventional sources of energy are those which have been in common use for a long time. Firewood and fossil fuels are the two main conventional energy sources. Whereas, Non-Conventional sources of energy are alternative forms of energy used in modern times. The use of renewable energy sources like organic waste, tide and wind energy come under non-conventional energy sources.
(ii)┬а The gaseous fuel formed from the conversion of organic waste such as dead plant, animal material, animal dung and kitchen waste is called biogas. Biogas is a mixture of methane and carbon dioxide and produces a huge amount of organic manure each year. Whereas, natural gas is extracted with petroleum deposits when crude oil is brought to the surface.
(iii)┬а Ferrous minerals contain iron such as iron ore, manganese and chromites. On the other hand, non-ferrous minerals do not contain iron like gold, silver, copper or lead.
(iv)┬а Metallic minerals contain metal in raw form. Bauxite and manganese are some examples of metallic minerals. While metals such as limestone, mica and gypsum do not contain metals elements and are called as Non-metallic minerals.