The void space in an $fcc$ structure is ..........

The anions $(A)$ of a $C_{p}A_{q}$ molecule form an $fcc$ lattice. Cations $(C)$ are positioned at the body center and half of the edge centers. The formula of the molecule is:

The volume occupied by the atoms in a unit cell of hexagonal close packing $(HCP)$ or cubic close packing $(CCP)$ is equal to:

Define: Packing Efficiency.

What is the total number of tetrahedral voids in $0.6 \ mole$ of a compound that forms a $hcp$ structure?

$Ga$ (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).