Into which kingdom would you classify a newly discovered unicellular, eukaryotic organism that moves using a flagellum?

A newly discovered unicellular eukaryotic organism that moves using a flagellum would be best classified in the Protista kingdom. Protists are eukaryotic organisms that cannot be classified as a plant, animal, or fungus. They are mostly unicellular, but some, like algae, are multicellular. I hope this is the answer that you were looking for.