What is the number of octahedral voids present in $0.2 \ mol$ of a compound forming $hcp$ structure?

Atoms of element $B$ form $hcp$ lattice and those of the element $A$ occupy $2/3$ of tetrahedral voids. What is the formula of the compound formed by the elements $A$ and $B$?

For the given close-packed structure of a salt made of cation $X$ and anion $Y$ shown below (ions of only one face are shown for clarity),the packing fraction is approximately
$\text{(packing fraction} = \frac{\text{Packing efficiency}}{100}\text{)}$

In a cubic close-packed $(ccp)$ structure,if there are $N$ spheres,what is the number of octahedral voids?

In a compound $XY$,the atoms of element $Y$ form a $ccp$ structure,while the atoms of element $X$ occupy $2/3$ of the tetrahedral voids. The molecular formula of the compound will be ..........

Calculate the void volume of a $bcc$ unit cell if the volume of the unit cell is $8.0 \times 10^{-23} \text{ cm}^3$.