The physical properties of the noble gases change in a regular way down group 0. The atoms get larger, the attractive forces between atoms get stronger, and so the boiling point rises. The density also increases down the group, so xenon is much denser than helium.
Approximate boiling points: helium -269 °C, neon -246 °C, argon -186 °C, krypton -152 °C and xenon -108 °C. All of them are colourless gases at room temperature, because their boiling points are far below room temperature (about 20 °C).
You can use this pattern to predict the properties of a noble gas you are not given. Radon is below xenon in group 0, so we predict that its boiling point is higher than -108 °C and that it is denser than xenon. Plotting boiling point against position in the group lets you read off a sensible estimate.
