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

• A. 1
• B. 3
• C. 2
• D. 4

Answer: (C)

In a body-centered cubic lattice, the conventional unit cell has atoms at the eight corners and one atom at the center. Corner atoms are shared among eight neighboring cells, so they contribute 8 × (1/8) = 1 atom to the unit cell. The atom at the center lies entirely inside the cell, contributing 1 more atom. Total = 1 + 1 = 2 atoms per conventional unit cell. For contrast, the primitive cell would contain only 1 atom, but the conventional cell in BCC contains 2.