What is the coordination number of $Zn^{2+}$ and $S^{2-}$ ions in the zinc blende $(ZnS)$ structure?

The number of nearest neighbours in a $BCC$ unit cell is

If the side length of a face-centered cubic $(fcc)$ unit cell of a metal is $400 \ pm$, the approximate radius of the metal atom in $pm$ is $(\sqrt{2} = 1.414)$.

An ionic compound is expected to have a tetrahedral structure if the radius ratio $r_{+} / r_{-}$ lies in the range of:

Find the radius of an atom in $fcc$ unit cell having edge length $393 \ pm$. (in $pm$)

In an $AgI$ crystal,$I^{-}$ ions form a close-packed structure. What percentage of the tetrahedral voids is occupied by $Ag^{+}$ ions?