What element has the symbol 'Rn'?

The story behind the answer

The symbol Rn stands for Radon, element 86. Radon is a noble gas (Group 18), colorless and chemically inert. The other options have different symbols: Rhenium is Re, Ruthenium is Ru, and Radium is Ra—so only Radon matches Rn.

Radon is a naturally occurring radioactive gas produced by the decay of uranium and radium in rocks and soil. It can accumulate in basements and is a leading cause of lung cancer after smoking—despite being invisible and odorless. Memory tip: most noble gases end in “-on” (neon, argon, krypton, xenon, radon), and “