Final answer:
Anthracite coal has the highest carbon content by weight, making it the most energy-dense and the highest grade of coal. It is preferred for high-heat applications and contributes less to acid rain pollution compared to other coal types.
Step-by-step explanation:
The rank of coal with the highest carbon content by weight is anthracite. Through natural processes involving burial under high pressure and temperatures for millions of years, plant materials are converted into coal, progressing from lignite, to sub-bituminous, to bituminous, and finally to anthracite. Anthracite coal has the highest carbon content and thus the highest energy content, making it the most desirable for applications requiring high heat, such as metallurgical refining. Furthermore, due to having a higher carbon concentration, anthracite releases less sulfur dioxide (SO2), which contributes to acid rain, than other types like bituminous coal, which contains greater amounts of sulfur due to pyrite (FeS2) particles.As more premium coal resources like anthracite get depleted, and we move towards mining lower-grade coals such as lignite, more mass needs to be removed to achieve the same energy output. It's important to note that despite its high quality, anthracite makes up a smaller portion of the world's coal reserves compared to lower-grade coals.