Which one possesses an antifluorite structure?

In the calcium fluoride structure,the coordination number of the cation and anion are respectively:

Which type of cubic lattice has the maximum number of atoms per unit cell?

The number of nearest neighbours and next nearest neighbours of an $Na^{+}$ ion in a crystal of $NaCl$ are respectively

$KBr$ crystallizes in a $fcc$ lattice (similar to $NaCl$). The second nearest neighbor of $K^+$ ion and its number are:

$A$ solid $A^{+}B^{-}$ has a $NaCl$ type close-packed structure. If the radius of the anion is $250 \ pm$, what should be the ideal radius of the cation in $pm$?