Question

How can we measure the radius for noble gases?

Answer 1

Hint : Any of the gaseous elements helium, neon, argon, krypton, xenon, and radon, occupying Group zero $(18)$ of the periodic table. They were long believed to be totally unreactive but compounds of xenon, krypton, and radon are now known.

Complete Step By Step Answer:
$-$ For noble gases radius is measured as van der Waals radius because these atoms are held together by weak van der Waals forces.
$-$ The Van der Waals radius of noble gases can be measured as these gases generally do not form compounds except Xenon.
$-$ The radius of an atom can only be found by measuring the distance between the nuclei of two touching atoms, and then halving that distance.

Additional Information:
The noble gases are used to form inert atmospheres, typically for arc welding, to protect specimens, and to deter chemical reactions. The elements are used in lamps, such as neon lights and krypton headlamps, and in lasers. Neon has many common and familiar applications: neon lights, fog lights, TV cine-scopes, lasers, voltage detectors, luminous warnings, and advertising signs. Helium is used in balloons, for deep-sea diving air tanks, and to cool superconducting magnets.

Note :
A full outer shell of electrons. Helium has two electrons in its outer shell and the rest have eight electrons. Because of their full outer shells, they are very inert and stable. They are gases under standard conditions. They are colorless and odorless. Their melting and boiling point are closed together giving them a very narrow liquid range.