$A$ compound is formed by two elements $A$ and $B$. The atoms of element $B$ form $ccp$ structure. The atoms of $A$ occupy $1/3$ of tetrahedral voids. What is the formula of the compound?

What is the percentage of unoccupied space in $fcc$ unit cell (in $\%$)?

The radius ratio of cation to anion for a triangular void is ....

Percentages of free space in cubic close packed structure and in body centered packed structure are respectively

The atomic radius of an $fcc$ unit cell is:

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