What is the percentage of unoccupied space in $fcc$ unit cell (in $\%$)?

In a crystalline solid,anion $B$ are arranged in $ccp$ lattice and cation $A$ occupy $50\%$ of the octahedral voids and $50\%$ of tetrahedral voids. What will be the formula of the crystalline solid?

$A$ compound of formula $A_2B_3$ has the $hcp$ lattice. Which atom forms the $hcp$ lattice and what fraction of tetrahedral voids is occupied by the other atoms?

The fraction of total volume occupied by the atoms present in a simple cubic unit cell is

If the anions $(A)$ form hexagonal closest packing and cations $(C)$ occupy only $2/3$ of the octahedral voids in it,then the general formula of the compound would be

In a close-packed structure of mixed oxides,the lattice is composed of oxide ions. One-eighth of the tetrahedral voids are occupied by divalent cations $(A^{2+})$,while one-half of the octahedral voids are occupied by trivalent cations $(B^{3+})$. The formula of the mixed oxide is: