An inert gas is one which does not react with other elements. The Noble gases and Nitrogen often do not react with many substances. Reed Switches are filled with a a mixture of inert gases to exclude contaminants, prevent oxidation of the contacts, and to prevent ice formation in low temperature applications.
An inert gas is a gas that does not undergo chemical reactions under a set of given conditions. The noble gases often do not react with many substances and were historically referred to as the inert gases. Inert gases are used generally to avoid unwanted chemical reactions degrading a sample. These undesirable chemical reactions are often oxidation and hydrolysis reactions with the oxygen and moisture in air. The term inert gas is context-dependent because several of the noble gases can be made to react under certain conditions.
Unlike noble gases, an inert gas is not necessarily elemental and is often a compound gas. Like the noble gases, the tendency for non-reactivity is due to the valence, the outermost electron shell, being complete in all the inert gases. This is a tendency, not a rule, as noble gases and other "inert" gases can react to form compounds.
The group 18 elements include helium, neon, argon, krypton, xenon and radon. They are referred to as noble gases or inert gases. The general configuration of the valence shell is ns2np6. All of these elements occur in a free state in the atmosphere. They are colourless, tasteless and odorless gases. They exhibit low melting and boiling points. They have high positive electron gain enthalpy and high ionization enthalpy.