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

$A$ compound is formed by elements $A$ and $B$. This crystallises in the cubic structure where the $A$ atoms are at the corners of the cube and $B$ atoms are at the body centres. The simplest formula of the compound is

$A$ unit cell of calcium fluoride has four calcium ions. The number of fluoride ions in the unit cell is

$Na$ and $Mg$ crystallize in $BCC$ and $FCC$ type crystals respectively,then the number of atoms of $Na$ and $Mg$ present in the unit cell of their respective crystal is

In a face-centered cubic $(FCC)$ unit cell,what fraction of an atom located at the face center is shared by one unit cell?

The structure of $TlCl$ is similar to $CsCl$. What would be the radius ratio in $TlCl$?