Radon is a gas, and gases don't have hardness in the same way that solids do. Hardness is a measure of a material's resistance to scratching or indentation, and these concepts don't apply to gases.

While radon is a noble gas, meaning it's unreactive, it can still be hazardous to human health due to its radioactivity.

Perhaps you're interested in a different property of radon? If so, please clarify your question and I'd be happy to help.