How many chloride ions are there around a sodium ion in a sodium chloride crystal?

The crystal structure of $AB$ is of $NaCl$ type. If the radius of the $A^+$ ion is $x \ pm$ and the radius of the $B^-$ ion is $y \ pm$, then the edge length of the unit cell will be ..........

An ionic compound has a unit cell consisting of $A$ ions at the corners of a cube and $B$ ions on the centres of the faces of the cube. The empirical formula for this compound would be

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

The number of equidistant oppositely charged ions in a sodium chloride crystal is

Explain the calculation of the number of atoms in a body-centered cubic $(bcc)$ unit cell.