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

In an ionic solid,anions $(B)$ are arranged in an $hcp$ array and cations $(A)$ occupy $\frac{2}{3}$ of the octahedral voids. What is the formula of the ionic compound?

The edge of unit cell of $FCC$ $Xe$ crystal is $620 \ pm$. The radius of $Xe$ atom is $..........$ $pm$.

$A$ compound forms an $hcp$ structure. What is the total number of tetrahedral voids formed in $0.8 \text{ mol}$ of this compound?

If the radius of the octahedral void is $r$ and the radius of the atoms in close packing is $R$,derive the relation between $r$ and $R$.

Which crystal lattice has the maximum packing efficiency?