In hexagonal close packing of spherer in three dimensions.

Options

A. In one unit cell there are 12 octahedral voids and all are completely inside the unit cell.
B. In one unit cell there are six octahedral voids and all are completely inside the unit cell
C. In one unit cell there are six octahedral void and of which three are completely inside the unit cell and other three are partially inside the unit cell
D. In one unit cell there are 12 tetrahedral voids, all are completely inside the unit cell

Answer

B

Explanation

HCP=AB AB AB….. Pattern repeat
For calculating voids between two layers A and B .
Total tetrahedral voids=12(represented by dots) out of which 8 are completely inside but rest are shared by other unit cells.
Total octahedral voids=6(represented by cross).All are completely inside.