Which kingdom is composed of a diverse array of single-celled prokaryotic organisms?

The kingdom that is composed of a diverse array of single-celled prokaryotic organisms is Eubacteria. This kingdom includes bacteria that have a relatively simple structure, lacking a nucleus and membrane-bound organelles, characteristic features of prokaryotic cells. Eubacteria are incredibly diverse, with various species that can be found in numerous environments, playing crucial roles in ecosystems, human health, and biotechnology.

Other kingdoms, such as Fungi, Plantae, and Protista, include organisms that are primarily eukaryotic, meaning they possess a nucleus and other membrane-bound organelles. Fungi are primarily multicellular (except for yeasts) and mainly decomposers. Plantae consists of multicellular photosynthetic organisms, and Protista includes a mix of organisms, some of which are unicellular and eukaryotic, including algae and protozoa. These distinctions are what make Eubacteria the kingdom specifically characterized by single-celled prokaryotic organisms.