Answer.
(a) Coal was formed by the decomposition of plants buried under the Earth's crust millions of years ago. Conversion of wood into coal is called carbonization. It is a very slow bio-chemical process. It takes place in the absence of air under high pressure and high temperature over a long period of time (about 500 millions of years). Wood contains about 40% carbon, so depending upon the extent of carbonization process, four types of coal are found. These types differ with respect to carbon content, volatile matter and moisture. Peat, lignite, bituminous and anthracite are the types of coals.
(b) The composition and uses of coal are represented in table given below.
Type of Coal
Carbon contents
Uses
Peat
60 %
It is inferior quality coal used in kiln.
Lignite
70 %
It is soft coal used in thermal power stations.
Bituminous
80 %
It is common variety of coal used as household coal.
Type of Coal
Carbon contents
Uses
Anthracite
90%
It is superior quality hard coal that is used in industry.