The ratio of close-packed atoms to tetrahedral holes in cubic close packing is

$Ga$ (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).

What is the minimum number of spheres required to develop a tetrahedral void?

What is the number of tetrahedral voids present in $0.5 \text{ mole}$ of a compound forming an $hcp$ structure?

The spinel structure consists of ............

When sodium is heated above $1000 \ K$,its crystal structure changes from $bcc$ to $fcc$. Assuming the metallic radius of the atom remains unchanged,the ratio of the fraction of volume occupied by atoms in $bcc$ and $fcc$ structures will be .......