noble gases
Family of chemical elements also called inert, as they are weakly reactant.
radon 
Highly radioactive noble gas that is used mainly in medicine (destroying cancerous tumors) and in predicting earthquakes.
xenon 
Rarest gas in the atmosphere; it is used mainly in discharge lamps, photoflash bulbs and lasers.
krypton 
Noble gas that is used in some incandescent lamps and in photography.
argon 
Most abundant of the noble gases; it is used especially in incandescent lamps and in welding (protective gas).
neon 
Noble gas that is used mainly in lighting (billboards, television tubes and fog lamps), but also as a liquid coolant.
helium 
The lightest of the noble gases is noncombustible and abundant in the stars; it is used especially in inflating aerostats (such as balloons and dirigibles).