Question

What is a noble gas

Answer 1

The term noble is an old chemical adjective for unreactive or incorruptible , thus gold was considered a ' noble metal' due to its resistance to corrosion. Noble gases are those gases in the periodic table in ,the same group, which have all their electron shells complete, so it is not necessary for them to bond with other substances in chemical reaction to complete and balance their outer electron shells by giving or receiving electrons (oxidation or reduction) or by covalent bonding.

They are by increase in period Helium, Argon, Neon,Krypton, Xenon, and Radon the last being radioactive and a source of pollution in areas with granite and other igneous rocks.
Helium has its uses as a non-flammable lighter than air gas, Argon whlch is the third most common atmospheric gas after nitrogen and oxygen is used in welding. All these gases can be ionised in electric lighting as coloured lights.
They are not totally unreactive the biggest will form weak hydrogen bonds with water.

So any of the gaseous elements helium, neon, argon, krypton, xenon, and radon, occupying Group 0 (18) of the periodic table are known as noble gas.They are called Noble gases since they don't react with other elements and are gases. ( they do actually react to a small degree with elements such a fluorine but they were called noble before we knew that ) They were long believed to be totally unreactive but compounds of xenon, krypton, and radon are now known.