Their outer energy levels are completely filled.
The class of noble gases (Helium, Neon etc. in group 18) There are two groups that come to mind when talking stability: the noble gases and the coinage metals. The noble gases (He, Ne, Ar, Kr, Xe, and Rn) are very chemically stable and do not readily form compounds. Note that although Radon is chemically stable, it's not stable from a nuclear standpoint and will decay (but it is not reactive in the chemical sense). The coinage metals (such as gold, silver, and copper) are very unreactive. Note that the further an element is from Au on the periodic table, the more reactive it is (obviously the Noble gases do not follow this trend).
All the elemental gases except for the noble gases come in molecules that are unstable. The noble gases are all stable, they have the maximum number of valence electrons that their outer shell can hold.
Noble gases have completely filled orbitals. They generally have 8 valence electrons (helium has only 2) and have stable electronic configuration. Hence they are chemically inert and generally donot form compounds / ions under normal conditions.
Noble gases don't react with other elements because of the stability of the outer hell. Helium has 2 electrons , 1s2 a full shell. the restt have an outer shell of 8 electrons the "octet". This gives neon a full valence shell, the rest of the heavier noble gases have an outer shell with 8 electrons which while it is is very stable and makes these gases very un-reactive it is not full.Compounds have been made for the noble gases heavier than neon. These compounds are all unstable and highly reactive and the first a xenon fluoride was made in 1962.
Noble gases have completely filled orbitals. They generally have 8 valence electrons (helium has only 2) and have stable electronic configuration. Hence they are chemically inert and generally donot form compounds under normal conditions. But it should be noted that at high temperature, xenon does form covalent compounds like XeF4, XeF6, XeOF2, XeOF4 etc.
The three main gases that come out of volcanoes are water vapor, carbon dioxide, and sulfur dioxide. These gases are released during eruptions and contribute to the volcanic activity and the formation of volcanic clouds.
Ionic compounds are generally more soluble in water than covalent compounds because ionic compounds dissociate into their constituent ions when they come into contact with water, forming ion-dipole interactions with water molecules. Covalent compounds do not readily dissociate in water, making them less soluble.
metaloids, halogens, metals, noble gases, carbon family and i think nitrogen family... there are more but these are the first that come to mind
easily liquifiable gases like Cl2, NH3,SO2,HCl are readily adsorbed because the critical temp of these gases are more. so it is easily liquified and adsorbed more readily.[critical temp is the minimum temp above which a gas cannot be liquified]easily liq. gases possess greater vanderwaals forces ,so they are adsorbed readily.these are the 2 reasons why these gases are readily adsorbed than permanent gases like H2, O2.N2 . etc
I am not sure entirely what you mean but there are lots of elements that go around in pairs, e.g hydrogen, oxygen, nitrogen amongst others.
the gases come from factories