Which of the classification groups would contain the most similar members?

The correct answer will be- species.

Explanation:

The hierarchical system of classification was proposed by the Carolus Linnaeus in the 18th century which categorized the organism into seven groups from the kingdom as the most inclusive group followed by the phylum, division, class, order, family, genus and species.

The species is the least inclusive group present at the bottom of the hierarchy system and exhibits the organism which are closely related to each other and share many similar characters.

Thus, species is the correct answer.