If you were looking at. unicelluar organism with a microscope, would you be looking at a prokaryotic o eukaryotic organism. how do you know ?

If your were looking at a prokaryotic cell it would have no nucleus or any other internal compartments however it would have a flagellum (tail). Where as a eukaryotic cell has internal compartments, a nucleus and no flagellum. 

That result from subduction of oceanic plates beneath lighter continental plates. most of the earth's volcanoes are located around the pacific ring of fire because that the location of most of the earth's subduction zones.

And a) oxygen i believe