Question

What is Van der waal radius?

Answer 1

It is half of the closest distance between two atoms that aren't bonded or within the same molecule. Typically the unit used is pm (picometers)

in other words
The Van der Waals radius is equal to one half the distance between two unbonded atoms when the electrostatic forces between them are balanced.

Answer 2

hey here is your answer

Covalent radius is half of the internuclear separation between the nuclei of two single-bonded atoms of the same species (homonuclear). While van der Waals radius is used to define half of the distance between the closest approach of two non-bonded atoms of a given element.

hope this helps you