Copper has face centered cubic (fcc) lattice with interatomic spacing equal to 2.54 Å. The value of lattice constant for this lattice is

2.54 Å 3.59 Å 1.27 Å 5.08 Å

3.59 Å

Given interatomic spacing = 2r = 2.54 Å $4r=\sqrt{2} a$, where a is lattice constant $2r=\frac{\sqrt{2}a}{2}=\frac{a}{\sqrt{2}}$ $a=2r\sqrt{2}= (2.54Å)(1.414) = 3.59Å$