18th group gases are called inert gases. Eg-He, Ne, Ar, Kr, Xe As the outermost shell of these gases are completely FILLED so, no gain or loss ELECTRON takes place. So these gases become chemically inert. So they are unreactive. Doest not so reactivity so have many applications 1.use in some reaction 2.used in PACKEDFOOD atoms 3.He is used in BALLONS due to its low weight