In a face-centered cubic lattice,a unit cell is shared equally by how many unit cells?

In a mixed oxide of two metals $X$ and $Y$,divalent $X^{2+}$ ions occupy $50\%$ of the tetrahedral voids,while trivalent $Y^{3+}$ ions occupy $50\%$ of the octahedral voids. The formula of the oxide is:

If all ions touching an axis passing through two opposite face-centres of unit cell are removed in $NaCl$ (rock salt) structure in which $Cl^{-}$ ions form $CCP$ and $Na^{+}$ ions occupy all octahedral voids,then the effective number of $Cl^{-}$ ions per unit cell is:

$A$ compound $M_pX_q$ has a cubic close packing $(ccp)$ arrangement of $X$. Its unit cell structure is shown below. The empirical formula of the compound is:
$M = \square$
$X = \bigcirc$

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

The coordination number of a sphere in a face-centered cubic $(fcc)$ lattice is .....