Which of the following are single-celled organisms that lack a nucleus and are classified as prokaryotes?

Bacteria are indeed classified as prokaryotes, which are single-celled organisms characterized by the absence of a nucleus. In prokaryotic cells, the genetic material is not enclosed within a nuclear membrane; instead, it exists as a single circular chromosome in a region called the nucleoid. Bacteria are one of the most well-known groups of prokaryotes and can be found in diverse environments across the globe, playing essential roles in processes such as nutrient cycling and decomposition.

In contrast, protozoa are eukaryotic microorganisms that have a defined nucleus and can be unicellular but are not classified as prokaryotes. Fungi, while they can also be unicellular (such as yeasts), belong to the eukaryotic domain and possess a defined nucleus and other organelles. Archaea, although they are also single-celled and prokaryotic like bacteria, represent a separate domain of life that often thrives in extreme environments and has distinct biochemical and genetic traits. However, in the context of this question, the most familiar and representative option classified as prokaryotes is indeed bacteria.