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

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 packing efficiency of the two-dimensional square unit cell shown below is (in $\%$)

What is the percentage efficiency of packing in $BCC$ structure (in $\%$)?

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

Consider the $bcc$ unit cells of the solid $1$ and $2$ with the position of atoms as shown below. The radius of atom $B$ is twice that of atom $A$. The unit cell edge length is $50\%$ more in solid $2$ than in $1$. What is the approximate packing efficiency in solid $2$? $........... \%$