IG meaning in Chemistry ?

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.

Purified argon and nitrogen gases are most commonly used as inert gases due to their high natural abundance (78.3% N2, 1% Ar in air) and low relative cost.

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 odourless gases. They exhibit low melting and boiling points. They have high positive electron gain enthalpy and high ionization enthalpy.