High grade (HG) and ultra high grade (UHG) anthracite are the highest grades of anthracite coal.
They are the purest forms of coal, having the highest degree of coalification, the highest carbon count and energy content and the fewest impurities (moisture, ash and volatiles).
Anthracite contains nearly 95% of carbon and is the purest form of coal so anthracite is the purest form of coal than any other forms.
Therefore, option B is correct.