Which of the following elements has an $hcp$ structure?

The percentage of unoccupied volume in a simple cubic cell is (in $\%$)

$A$ compound is formed by $X$ and $Y$ elements. Atoms of $Y$ (anions) form $hcp$ lattice. Atoms of $X$ (cations) are in some octahedral holes. The formula of the compound is $XY_3$. What is the fraction of octahedral holes unoccupied by $X$?

Calculate the void volume of a $bcc$ unit cell if the volume of the unit cell is $8.0 \times 10^{-23} \text{ cm}^3$.

In a face-centred cubic $(FCC)$ unit cell,what is the total volume occupied by the atoms?

The percentage of vacant space for $bcc$ unit cell is ............. $\%$