In hexagonal close packing of spherer in three dimensions.

Options

A. In one unit cell there are 12 octahedral voids and all are completely insdie 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 voids and of which three are completely insdie the unit cell and other three are from contributions of octahedral voids which are partially inside the unit cell
D. In one unit cell there are 12 tetradhedral voids all are completely inside the unit cell.

Explanation

hcp=AB AB AB..... Pattern repeaet
For calculating voids between two layers A and B, Total tetrahedral voids =12 (represented by "o") out of which 8 are completely inside but rest are shared by other unit cells. Tota octadhedral voids=6 (represented by "O"). All are completely inside.