What is the criterion for classification of organisms as belonging to kingdom Monera or Protista?

Organisms which are prokaryotes belong to the kingdom Monera. On the other hand, organisms which are eukaryotes and unicellular belong to the kingdom Protista

Monera or Protista are formed on the basis of their cell structure, mode and source of nutrition and body organisation.

The organisms belonging to Kingdom Monera are unicellular and prokaryotic whereas the organisms belonging to Kingdom Protista are unicellular and eukaryotic.

The organisms which do not possess well defined nucleus, organells and multicelluar body desings are grouped under the kingdom Monera. The organisms which are nuclellular and eukaryotic are grouped under the Kingdom Prostia.