Give two examples of metals that crystallize in the $hcp$ (hexagonal close-packed) structure.

The packing efficiency of simple cubic $(sc)$, body-centred cubic $(bcc)$ and cubic close packing $(ccp)$ lattices follow the order:

In a binary compound,atoms of element $A$ form a $hcp$ structure and those of element $M$ occupy $2/3$ of the tetrahedral voids of the $hcp$ structure. The formula of the binary compound is

$A$ mineral consists of a cubic close-packed structure formed by $O^{2-}$ ions,where half the octahedral voids are occupied by $Al^{3+}$ and one-eighth of the tetrahedral voids are occupied by $Mn^{2+}$. The chemical formula of the mineral is

If the anion $(A)$ forms a hexagonal closest packing and the cation $(C)$ occupies only $2/3$ of the octahedral voids in it,then the general formula of the compound is :-

In a face-centred cubic arrangement of $A$ and $B$ atoms,$A$ atoms are at the corners of the unit cell and $B$ atoms are at the face centres. If three of the $B$ atoms are missing from the face centres in the unit cell,what is the simplest formula of the compound?