$A$ metal oxide crystallises in a hexagonal close-packed $(HCP)$ array of oxide ions with two out of every three octahedral holes occupied by metal ions. The formula of the metal oxide is:

$A$ compound is formed by two elements $A$ and $B$. The element $B$ forms a cubic close-packed $(CCP)$ structure and atoms of $A$ occupy $\frac{1}{3}$ of the tetrahedral voids. If the formula of the compound is $A_x B_y$,then the value of $x+y$ is:

$A$ compound is formed by elements $A$ and $B$. Element $B$ forms an $HCP$ lattice,and element $A$ occupies $2/3$ of the tetrahedral voids. What is the formula of the compound formed by $A$ and $B$?

The number of octahedral void$(s)$ per atom present in a cubic close-packed structure is

Find the void volume of $fcc$ unit cell in $cm^3$ if the volume of $fcc$ unit cell is $1.25 \times 10^{-22} \ cm^3$.

What is the percentage of unoccupied volume in $BCC$ structure (in $\%$)?