Question:

Tungsten crystallizes in body centered cubic unit cell. If the edge of the unit cell is 316.5 pm, what is the radius of tungsten atom?

It is a BCC, for which radius is given by: r = √3/4 × a
a = 316.5 pm
Substituting the value of a we get,
Radius = √3/4 × 316.5 = 137.04 pm