The correct option is C TvZeff=2
Total no. of spheres in a hcp unit cell Zeff=(12×16)+(2×12)+3=6
(12×16) is for corners atoms of two hexagonal layers
(2×12) is for the centre atoms of two hexagonal layers
3 is for the atoms of middle layer
In hcp, there are total 12 tetrahedral voids out of which 8 tetrahedral voids are completely inside the unit cell and 12 voids are present at the edge centres.
Contribution of each edge centre particle is 13.
So, the total number of tetrahedral voids in hcp lattice are :
Also, There are six octahedral voids which are present completely inside the unit cell. Each fully contributes to the unit cell.