A compound forms a hexagonal close-packed (HCP) structure. The total number of octahedral and tetrahedral voids per unit cell in this structure is:
Correct: A
In an HCP structure, the effective number of atoms per unit cell (Z) is 6.
For any close-packed structure (HCP or FCC), the number of octahedral voids is equal to the effective number of atoms (Z), and the number of tetrahedral voids is twice the effective number of atoms (2Z).
Since Z for HCP is 6:
Number of octahedral voids = Z = 6
Number of tetrahedral voids = 2Z = 2 × 6 = 12
Therefore, an HCP unit cell contains 6 octahedral voids and 12 tetrahedral voids.