* Single-celled: This immediately eliminates the kingdoms that are primarily multicellular:

* Animalia (animals)

* Plantae (plants)

* Fungi (fungi)

* New life form: This implies it's something distinct from known organisms.

This leaves us with:

* Bacteria: A vast and diverse kingdom of single-celled prokaryotes (lacking a nucleus).

* Archaea: Another group of single-celled prokaryotes, often found in extreme environments.

* Protista: A diverse kingdom of mostly single-celled eukaryotes (possessing a nucleus).

Therefore, the new life form could potentially belong to any of these three kingdoms: Bacteria, Archaea, or Protista.

To determine which is most likely, the scientist would need to investigate further, looking at features like:

* Cell structure: Does it have a nucleus? Other internal structures?

* Metabolism: How does it obtain energy?

* Genetics: What is its genetic makeup like?

The answers to these questions would provide strong clues about the kingdom classification.