Are He,Ne,Ar,Kr,Xe and Rn the only known noble gases?
As per the latest data available, apart from Helium, Neon, Argon, Krypton, Xenon and Radon, no other noble gas has been identified. These six are the only known noble gases that are universally recognised. Also note that the periodic table lists all the elements that are known till date. There is no such element which is known and is not listed in the periodic table.