Radon is radioactive.its nucleus isnt stable.then y is it a noble gas?

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radon bcoms stable when it reaches lead.radon also has isotopes.can somebdy also temme how radoiactive elements combine?i mean how can they when they have such unstable nucleus?pls give configuration radon emits alpha particles .also the prtotons n neutrons gotta b balanced in no.so if the protons go so do the elctrons.hows is it stable