All eukaryotic unicellular organisms belong to:

The correct option is B

Protista

The correct option is B.

Explanation of correct option:

1. All unicellular eukaryotes come under the kingdom Protista.
2. Such organisms have well-defined nuclei and membrane-bound organelles.
3. They reproduce asexually by cell fusion and sexually by zygote formation.
4. They are primarily aquatic and microscopic.

Explanation of incorrect options:

Option A:

1. Monera consists of prokaryotes.
2. They are bacteria that are the most abundant microorganisms.

Option C:

1. Multicellular eukaryotes which do not perform photosynthesis come under the kingdom Fungi.
2. The only exception is yeast.

Option D:

1. Bacteria come under the kingdom Monera.
2. They occur everywhere and show the most extensive metabolic diversity.

Final answer: All unicellular eukaryotic organisms belong to Protista.