Question

As the rank of coal increases, the proportion of carbon in it ______.

a) decreases
b) stays the same
c) increases
d) bogus question: the "rank" refers to the proportion of silica in the coal.

Answer 1

As the rank of coal increases, the proportion of carbon in it increases.

Step-by-step explanation:

As the rank of coal increases, the proportion of carbon in it increases.

The different ranks of coal, from lowest to highest, are lignite, sub-bituminous, bituminous, and anthracite. As the rank increases, the carbon content increases and other impurities, such as sulfur and moisture, decrease.

For example, lignite coal has the lowest carbon content, ranging from 25-35%, while anthracite coal has the highest carbon content, ranging from 86-97%.