Define: Packing Efficiency.

The molecular formula of a crystalline solid is $X_3Y_2$. Atoms of $Y$ form $ccp$ lattice,and atoms of $X$ occupy $50\%$ octahedral voids and $x\%$ of tetrahedral voids. What is the percentage of unoccupied tetrahedral voids?

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 volume of $fcc$ unit cell in $cm^3$ if void volume of it is $4.16 \times 10^{-24} \ cm^3$.

$A$ metal crystallizes in a simple cubic unit cell. Calculate the void volume of the unit cell. $[a = 3.36 \times 10^{-8} \text{ cm}]$