An organism that is only one cell big and has a nucleus is most likely a member of which kingdom? ​

Protista

Explanation:

Taxonomy can be defined as the process of naming, classification and description of living organisms such as plants and animals. Thus, the biological classification of living organisms based on similarities or characteristics such as eyes, number of legs, etc., is generally referred to as taxonomy.

Basically, taxonomy helps scientist to have a good understanding and knowledge when studying various organisms.

Furthermore, the eight (8) biological classification (taxonomy) used for grouping and organizing organisms are; kingdom, domain, phylum, family, order, class, species and genus.

An organism that has only one cell, big and has a nucleus is most likely a member of Protista. Thus, a Protista such as euglena, paramecium, amoeba, etc., have a nucleus and are unicellular.

A unicellular organism refers to a living organism that possess a single-cell while a multicellular organism has many (multiple) cells.