Which has the least similarity?

The correct answer is Phylum

Explanation:

• In biological classification, the hierarchy of taxonomic ranks is used to organize and categorize organisms in a systematic manner.
• Each rank represents a different level of organization and relationship among organisms.
• The main taxonomic ranks include Domain, Kingdom, Phylum/Division, Class, Order, Family, Genus, and Species.
• As we go higher from species to kingdom, the number of common characteristics goes on decreasing.
• The lower the taxa, the more are the characteristics that the members within the taxon share.
• The higher the category, greater is the difficulty of determining the relationship to other taxa at the same level. 

Fig: Taxonomic categories showing hierarchial arrangement in ascending order.

In conclusion, Phylum has the least similarity among its members compared to Species, Family, and Genus because it is a higher taxonomic rank that groups organisms based on very broad characteristics.