Why are nobel gases grouped together on the periodic table?

Nobel gases also referred as inert gases, they are grouped together because they are the most stable elements. This explains why they are nonreactive. They do not form chemical bonds because they only have a little tendency to either gain or lose an electron, since they have 8 electrons in the outer shell (except for helium as it has 2 electrons in the outer shell). As a result, they do not react with any other element in the periodic table.

the reaction mixture contains some ammonia, plus a lot of unreacted nitrogen and hydrogen. the mixture is cooled and compressed, causing the ammonia gas to condense into a liquid. the liquefied ammonia is separated and removed. the unreacted nitrogen and hydrogen are then recycled back into the reactor .