Coordination number of $Zn^{2+}$ in $ZnS$ (zinc blende) is

The coordination number for $Cu$ (Copper) in its crystal structure is:

Choose the correct statement for the given cubical structure.

$CsBr$ has a $bcc$ structure. If the edge length is $4.3 \ \overset{\circ}{A}$,what is the minimum distance between $Cs^+$ and $Br^-$ ions in $\overset{\circ}{A}$?

$A$ cubic lattice has atoms of $A$ at the body centre,atoms of $B$ at the corners of the cube and atoms $C$ at all the face centres. What is its formula?

The structure of $Na_2O$ crystal is