Unit Cells

Radius ratio= As it lies in the range 0.414 - 0.732, the coordination number will be 6

In a unit cell, atoms located at the corners are shared by eight adjacent unit cells. Hence, each corner atom contributes only of its total volume to a single unit cell. Therefore, the correct answer is option (D).

In a hexagonal close-packed (hcp) unit cell, there are: - 12 atoms on the corners of the hexagon, each shared by 6 unit cells, contributing per corner atom. - 2 atoms in the face centers, each shared by 2 unit cells, contributing per face-centered atom. - 2 atoms entirely within the unit cell. Thus, the total number of atoms per unit cell is: Therefore, there are 6 atoms per unit cell in an hcp structure.