What is the percentage of empty space in a $bcc$ unit cell (in $\%$)?

The correct option for the number of tetrahedral and octahedral voids in a hexagonal primitive unit cell is:

Which of the following metals has an $hcp$ crystal structure?

$Ga$ (atomic mass $70 \, u$) crystallizes in a hexagonal close packed structure. The total number of voids in $0.581 \, g$ of $Ga$ is $\dots \dots \dots \dots \dots \times 10^{21}$. (Round off to the Nearest Integer).

$A$ 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

In a close-packed lattice,how does the size of an octahedral void compare to that of a tetrahedral void?