Calculate the packing efficiency of FCC.

In FCC, 4 atoms are present per unit cell. Volume occupied by atoms = 4×43πr34 \times \frac{4}{3}\pi r^3. Volume of cube = a3a^3, and a=22ra = 2\sqrt{2}r. Packing efficiency = Volume occupiedTotal volume×100\frac{\text{Volume occupied}}{\text{Total volume}} \times 100 = 74%.