Which of the following is a unicellular kingdom that contains a nucleus and organelles?

The correct choice is Protista, which is classified as a unicellular kingdom that possesses a nucleus and organelles. Organisms within this kingdom, such as amoebas and paramecia, are eukaryotic, meaning they have complex cells with a defined nucleus enclosed by a nuclear membrane, as well as various organelles that perform specific functions.

In contrast, Archaebacteria and Eubacteria belong to the prokaryotic domains, which are characterized by the absence of a true nucleus and membrane-bound organelles. These organisms have simpler cell structures. Fungi, while they are eukaryotic and do contain a nucleus and organelles, are primarily multicellular (with some unicellular forms, like yeast) and are classified in a different kingdom separate from Protista. Thus, Protista is the only option that fully meets the criteria of being a unicellular kingdom with a nucleus and organelles.