If the atomic radius of a calcium crystal is 180 pm, what is the length of the edge of the unit cell? (the calcium crystal forms

Calcium crystal has a face center cubic (FCC) structure. For FCC structure,
relation between edge length (a) and radius (r) is
                                                       a = 2√2 r
Given: r = 180 pm
Therefore, a = 2√2 180
                     = 2 x 1.141 x 180
                     = 410.76 pm

The length of the edge of the Ca unit cell is 410.76 pm.