The packing efficiency of the face-centered cubic $(fcc)$,body-centered cubic $(bcc)$,and simple/primitive cubic $(pc)$ lattices follows the order:

If a compound (oxide) has an $hcp$ arrangement and the cations $M$ occupy two-thirds of the octahedral voids,the formula of the compound is:

Explain tetrahedral and octahedral voids.

Hexagonal close packing $(HCP)$ is found in the crystal lattice of:

In which of the following crystals are all the tetrahedral voids occupied?

$Ga$ (atomic mass $70 \, u$) crystallizes in a hexagonal close packed structure. The total number of voids in $0.581 \, g$ of $Ga$ is $\dots \dots \dots \dots \dots \times 10^{21}$. (Round off to the Nearest Integer).