The correct option is A decrease
The seven obligate categories in descending order of the taxonomic hierarchy include kingdom, phylum or division, class, order, family, genus and species.
As we go from species to kingdom, the number of common characteristics decreases.
For example, any genus (lower grade of classification) has members with more similarities as compared to a family (a higher grade of classification) which has members with fewer similarities among them.
On the contrary, as we go from kingdom to species, the number of common characteristics increases.
So, the correct answer is option A.