What is the crystal structure of $Na_2O$?

An element has a face-centred cubic $(fcc)$ structure with a cell edge of $a$. The distance between the centres of two nearest tetrahedral voids in the lattice is

By increasing the pressure on $NaCl$ crystal,its coordination number will

What is the coordination number of sodium in $Na_2O$?

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

The radius of $Na^{+}$ is $95 \, pm$ and the radius of $Cl^{-}$ ion is $181 \, pm$. What is the coordination number of $Na^{+}$?