Answer:
Protista
Explanation:
In biology, there are said to be six different kingdoms that an organism can be classified under. They include Animalia, Plantae, Fungi, Protista, Archaea/Archaebacteria, and Bacteria/Eubacteria.
With this in mind, you say that a unicellular (single-celled) organism without a nucleus was found in pond water. This would point to the Protista kingdom, which are also known as protists. These organisms are single-celled beings with no big nucleus that are typically found in environments like ponds.
Hope this helped! I will take my 100,000 dollars via wire transfer (or just give this answer branliest)