Final answer:
The kingdom composed exclusively of unicellular organisms without a nucleus is Monera.
Step-by-step explanation:
The kingdom made up of only unicellular organisms is Monera. The term prokaryotes refers to unicellular organisms that have no nucleus, which is characteristic of the organisms in the Monera kingdom, including bacteria and archaea. In contrast, the kingdom Protista includes many unicellular organisms as well, but also contains some multicellular organisms like giant algae. Kingdom Animalia includes only multicellular organisms, and Kingdom Plantae also consists of multicellular organisms that mainly perform photosynthesis.