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

In the $NaCl$ crystal structure,how many chloride ions surround each sodium ion?

Potassium fluoride $(KF)$ has a $NaCl$ type structure. If the edge length of the unit cell is $a$,what is the distance between $K^+$ and $F^-$ ions?

If the pressure on a $NaCl$ structure is increased,then its coordination number will

For tetrahedral coordination number,the radius ratio $\frac{r_{c^+}}{r_{a^-}}$ is

In a simple cubic unit cell,how many unit cells share each lattice point located at the corner?