Question

What is meant by gram positive and negative And arches only live in extreme conditions

Answer 1

Medical Definition of Gram-positive. Gram-positive: Gram-positive bacteria retain the color of the crystal violet stain in the Gram stain. This is characteristic of bacteria that have a cell wall composed of a thick layer of a particular substance (called peptidologlycan).

Archaea are also diverse, but none are pathogenic and many live in extreme environments.
Archaea
Domain Archaea contains 4 major groups. Intriguingly, so far, no archaea that are human pathogens have yet been discovered.
Archaea do live in our bodies and those of animals—for instance, in the gut—but all of them seem to be harmless or beneficial. Although there are hypotheses, no one yet knows exactly why archaea are all "friendly," i.e., why no disease-causing species have evolved.start superscript, , end superscript
Alongside the archaea that enjoy the comfy environment of the human gut, there are many extremophile species that live in much more inhospitable places. These include volcanic hot springs, undersea hot vents, and very salty places like the Dead Sea.