The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
The biological classification follows a hierarchical order, that includes seven obligate categories kingdom, division or phylum, class, order, family, genus and species. To further distinguish the individuals of a single category into different groups with increased specificities, sub-categories like sub-kingdom, superphylum or super division, superclass, subclass, superorder, suborder, superfamily, subfamily, tribe, subspecies, variety etc. have been added.
Hence, the correct answer is option B.