The radius ratio of cation to anion for a triangular void is ....

Which of the following metals crystallizes in a hexagonal close-packed $(hcp)$ structure?

In a solid compound,the oxide ions are arranged in $CCP$. Cations $A$ occupy $1/6^{th}$ of the tetrahedral voids and cations $B$ occupy one third of the octahedral voids. The probable formula of the compound is

$A$ metal crystallizes in a lattice having $AB AB AB$ sequence of layers. This arrangement of spheres corresponds to which type of packing,and what is the percentage of empty space (void volume) in this lattice?

What is the formula for packing efficiency?

In a crystalline compound,$A$ atoms occupy all corners,$B$ atoms occupy all face-centered positions,$C$ atoms occupy all edge centers,and $D$ atoms occupy all tetrahedral voids formed by $A$ and $B$ atoms. Find the formula of the compound.