Question:

Copper crystallizes in fcc with a unit cell length of 361 pm. What is the radius (in pm) of a copper atom?

109

181

127

157

For FCC the relation between radius and the edge length is as follows:
√2a = 4r
∴r = √2 × a / 4 = √2 × 361 / 4 = 127.6 pm