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 competely inside the unit cell.
C. In one unit cell there are six octahedral voids and of which three are completely inside 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` tetrahedral voids, all are completely inside the unit cell.

Answer

B

Explanation

b. `hcp = AB AB AB …` pattern repeat
For calculation voids between two layers `A` and `B`,
Total tetrahedral voids `= 12` (represented by `"@"`) out of which `8` are completely inside but rest are shared by other unit cells.
Total octahedral voids `= 6` represented by `"●"`). All the are completely inside.