What is the percentage of void space in $hcp$ and $ccp$ structures (in $\%$)?

$A$ compound is formed by elements $P$ and $Q$. Atoms of $Q$ are in $ccp$ arrangement. If $P$ occupies all the tetrahedral voids,what is the formula of the compound?

$A$ solid element (metal) crystallises in $ABABAB$ type packing in three dimensions. If the density of the element and its atomic radius are $5.0 \ g/cm^3$ and $100\sqrt{2} \ pm$ respectively, the atomic mass of the element is $(N_A = 6 \times 10^{23} \ mol^{-1})$

Atoms of element $X$ form $hcp$ lattice and those of element $Y$ occupy $\frac{2}{3}$ of its tetrahedral voids. The percentage of element $X$ in the lattice is ..... . (Nearest integer)

What fraction of one edge-centred octahedral void lies in one unit cell of $fcc$?

In the closest packing of atoms,there are