Using microscope slides and dipping them into the boiling hot springs at yellowstone national park, scientists were able to collect these organisms. they are unicellular, prokaryotes with a cell wall. what are they?

The correct answer is-

Archaebacteria.

Archaebacteria is a domain of unicellular micro organisms, which constitute a group of most primitive forms of prokaryotes ( that is devoid of nucleus and membrane bound subcellular organelles). The organism under this domain are adapted to survive under extremely harsh conditions ( therefore also called extremophiles) such as boiling mud around volcano, hotsprings.

Example- Methanogens.

In the question, scientists were able to collect the organisms by using microscope slides, which were dipped into the boiling hot springs.

Thus, it represents the organisms collected were Archaebacteria.