(B) The noble gases are $He$,$Ne$,$Ar$,$Kr$,$Xe$,and $Rn$. All noble gases except $Rn$ (Radon) are present in the atmosphere. $Rn$ is a radioactive el

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(B) The noble gases are $He$,$Ne$,$Ar$,$Kr$,$Xe$,and $Rn$. All noble gases except $Rn$ (Radon) are present in the atmosphere. $Rn$ is a radioactive element formed by the radioactive decay of radium $(^{226}_{88}Ra \rightarrow ^{222}_{86}Rn + ^{4}_{2}He)$. Therefore,$Rn$ does not occur in the atmosphere.