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

$A$ and $B$ atoms in a crystal are positioned at the corners and face centers respectively. What is the formula of the crystal?

For an ionic crystal of the type $AB$,the value of the limiting radius ratio is $0.40$. This value suggests that the crystal structure should be:

$A$ cubic solid is made of two elements $P$ and $Q$. Atoms of $Q$ are at the corners of the cube and $P$ at the body-centre. What is the formula of the compound? What are the coordination numbers of $P$ and $Q$?

The structure of $TlCl$ is similar to $CsCl$. What is the coordination number of $Tl^{+}$?

An ionic compound $AB$ has $ZnS$ type structure. If the radius of $A^{+}$ is $22.5 \ pm$, then the ideal radius of $B^{-}$ would be .............. $pm$.