Group 18 Elements Noble Gases

Step 1: Fact check.
Among noble gases, radon (Rn) is naturally radioactive (formed in the decay chain of U and Th).
Step 2: Eliminate others.
He, Ne, and Xe are stable (non-radioactive) isotopes under normal conditions.
Step 3: Conclusion.
Therefore, the radioactive noble gas is Rn.

Step 1: Known noble-gas compounds.
Xenon forms many stable compounds (e.g., XeF , XeF , XeF , XeO , XeO ).
Step 2: Compare others.
He, Ne are extremely inert; Ar forms very few compounds (e.g., HArF at very low temperature).
Step 3: Conclusion.
Hence, the noble gas with maximum known compounds is Xenon.