Being monoatomic, the atomic radii of noble gasses are very small compared to the covalent radii of other elements.
False
Determination of the atomic radius of an atom is very difficult because it is very small and electrons surrounding the atom do not have a sharp boundary.
That's why we always try to estimate the covalent radius which is usually lesser than the individual atom's radius.
Generally, noble gasses are inert.
That's why they are monoatomic. Being monoatomic and non-reactive, they do not have covalent radii.
Van der Waals radii are estimated for noble gasses, that is why their values are very large.