Which statements about ionic crystal structures are correct?

AIn $ZnS$ each $Zn X^{2 +}$ ion is surrounded tetrahedrally by 4 sulfide ions.
BIn $CaF X_{2}$ the coordination number of $Ca X^{2 +}$ is 8 and that of $F X^{-}$ is 4.
CIn $Na X_{2} O$ the $Na X^{+}$ ions occupy the octahedral voids of the $O X^{2 -}$ lattice.
DIn the CsCl unit cell, the number of formula units is 2.

Answer: A, B

Zinc blende has 4:4 tetrahedral coordination. In fluorite,

Ca X^{2 +}

(fcc) has CN 8 and

F X^{-}

CN 4. In antifluorite

Na X_{2} O

Na X^{+}

fill the tetrahedral voids (8 per cell). CsCl has

Z = 8 \times \frac{1}{8} = 1

formula unit per cell, so C and D are wrong.