Bacteria are classified in the Prokaryote domain.
To understand why, we need to look at the fundamental differences between the domains of life. There are three main domains: Bacteria, Archaea, and Eukarya. Bacteria are unicellular organisms that lack a nucleus and membrane-bound organelles, which categorizes them as prokaryotic cells. In contrast, eukaryotic cells, found in organisms like plants, animals, and fungi, have a defined nucleus and complex cellular structures. Since bacteria do not possess these features, they fall under the prokaryote classification. Therefore, the correct answer is option b) Prokaryote.