The correct answer is: b) Bituminous coal.
Bituminous coal is the most abundant type of coal found in Assam. It is a soft coal that is black or dark brown in color. It is used to generate electricity, produce coke, and make chemicals.
Lignite is a type of coal that is less mature than bituminous coal. It is brown or black in color and has a high moisture content. It is used to generate electricity and produce chemicals.
Sub-bituminous coal is a type of coal that is between lignite and bituminous coal in maturity. It is black or dark brown in color and has a lower moisture content than lignite. It is used to generate electricity and produce chemicals.
Anthracite is the most mature type of coal. It is black in color and has a low moisture content. It is used to generate electricity and produce steel.
In conclusion, bituminous coal is the most abundant type of coal found in Assam. It is a soft coal that is black or dark brown in color. It is used to generate electricity, produce coke, and make chemicals.