Inert gas and Radon

Inert gas noun - Any of the chemically inert gaseous elements of the helium group in the periodic table.

Radon and inert gas are semantically related. In some cases you can replace term "Radon" with "Inert gas", this terms are similar.

Radon noun - A radioactive gaseous element formed by the disintegration of radium; the heaviest of the inert gasses; occurs naturally (especially in areas over granite) and is considered a hazard to health.

Inert gas and radon are semantically related. You can use "Inert gas" instead a noun "Radon".