Calculate the volume occupied by all particles in an $fcc$ unit cell if the volume of the unit cell is $1.6 \times 10^{-23} \ cm^3$.

Atom $X$ occupies the $fcc$ lattice sites as well as alternate tetrahedral voids of the same lattice. The packing efficiency (in $\%$) of the resultant solid is closest to

In chrysoberyl,a compound containing beryllium,aluminium and oxygen,oxide ions form a cubic close-packed structure. Aluminium ions occupy $\frac{1}{4}$ of the octahedral voids and beryllium ions occupy $\frac{1}{8}$ of the tetrahedral voids. The formula of the compound is

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

Atoms of element $X$ form $hcp$ lattice and those of element $Y$ occupy $\frac{2}{3}$ of its tetrahedral voids. The percentage of element $X$ in the lattice is ..... . (Nearest integer)

In a face-centered cubic $(FCC)$ close-packed structure,the third layer covers the ..... voids created between the first and second layers.