Question

The hardest type of coal is:
a.) bituminous
b.) anthracite
c.) sub-bituminous
d.) lignite

Answer 1

Hint: The coal with the highest carbon content is the hardest type of coal and is the best and cleanest type of coal. The four main types of coal are Anthracite, Lignite, Bituminous and sub-bituminous. Also the hardest type of coal contains the least amount of moisture.

Step by step answer:
Anthracite is also known as hard coal. It is a hard, compact variety of coal that has a sub-metallic lustre. It has the highest carbon content and the fewest of impurities. It is also the highest energy density among all types of coal and is ranked the highest in the category of coals.

Bituminous is also known as black coal and is relatively soft coal. It contains a tar-like substance called bitumen or asphalt and is higher quality than lignite coal, but it is poorer in quality than anthracite. It is usually formed by high pressure exerted on lignite and its coloration varies from black to dark brown

Lignite is also known as brown coal and it is a soft brown combustible sedimentary rock which is formed from naturally compressed peat. Its rank is the lowest in the category of coal due to its relatively low heat content it has a carbon content of around 20% to 35 %. It is mined all around the world and is used exclusively as fuel for steam electric power generation. This type of coal is the most harmful to health.

Sub-bituminous coal is a kind of coal which has properties ranging from those of lignite to those of bituminous. This is primarily used as fuel for steam electric power generation and its colour varies from dull or dark brown to black. It is a soft, crumbly coal and it lies in the lower end of the category of coals. Sub-bituminous coals with bright jet-black, hard and relatively strong rocks lie in the upper end category of coals. They contain 15% to 30% moisture by weight and they have a relatively low density and high water content. They might be susceptible to spontaneous combustion if they are not packed densely during storage to exclude free air flow between them.

Hence, Anthracite is the hardest type of coal. Therefore, the correct option is Option B.

Note: The grade of coal depends on its carbon content. The coal with the highest carbon content is the cleanest because it leads to minimum loss. The harder coals contain more carbon than softer coals because the moisture content in these kinds of coal are very low.