Question

Select the correct statement(s) related to hexagonal close packing of identical spheres in three dimensions.

• 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 out 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. Co-ordination number of every sphere is $12$ in hcp lattice.

Answer 1

Answer: (B), (D)

The correct options are
B In one unit cell, there are six octahedral voids and all are completely inside the unit cell.
D Co-ordination number of every sphere is $12$ in hcp lattice.

The following are true for hexagonal closed packing of identical spheres in three dimensions:
(1) In one unit cell, there are six octahedral voids and all are completely inside the unit cell.
(2) Co-ordination number of every sphere is $12$ in hcp lattice. Each atom is surrounded by $6$ atoms in the plane, $3$ atoms above the plane and $3$ atoms below the plane.