If the coordination number of an element in its crystal lattice is $8$,what will be its packing structure?

In a face-centered cubic lattice of $X$ and $Y$ atoms,$X$ atoms are present at the corners while $Y$ atoms are at the face centers. If two atoms of $X$ are missing from the corners,what is the formula of the compound?

What is the nature of octahedral holes (voids)?

For a tetrahedral structure,the limiting radius ratio $r_c^+ / r_a^-$ is .......

An element crystallizes in a $bcc$ lattice. The number of nearest neighbors of the element is

The radius of divalent cation $A^{+2}$ is $94 \, pm$ and divalent anion $B^{-2}$ is $146 \, pm$. The structure of compound $AB$ is