In which kingdom would you classify the archaea and nitrogen-fixing organism, if the five-kingdom system of classification is used :

In Whittaker's five-kingdom system, kingdom Monera includes all prokaryotes (organisms without a true nucleus and membrane-bound organelles).
Archaebacteria (archaea), such as methanogens, halophiles and thermoacidophiles, are prokaryotes.
Nitrogen-fixing organisms such as Rhizobium, Azotobacter and cyanobacteria (Nostoc, Anabaena) are also prokaryotes.
So both are classified in kingdom Monera.