How many atoms are contained in one conventional unit cell of a face-centered cubic lattice?

• A. 2
• B. 1
• C. 3
• D. 4

Answer: (D)

In a face-centered cubic lattice, count atoms by how much of each atom belongs to the conventional unit cell. Corner atoms are shared by eight neighboring cells, so eight corners contribute 8 × 1/8 = 1 atom to the cell. Face-centered atoms are shared by two cells, so the six faces contribute 6 × 1/2 = 3 atoms. Together, 1 + 3 equals four atoms per conventional unit cell.