Question

In which of the following structure coordination number for cations and anions in the packed structure will be same?

• A. $C{l}^{-}$ ions from $fcc$ lattice and $N{a}^{+}$ ions occupy all octahedral voids of the unit cell.
• B. $C{a}^{2+}$ ions from $fcc$ lattice and $F^{-}$ ions occupy all eight tetrahedral voids of the unit cell.
• C. $O^{2-}$ ions from $fcc$ lattice and $N{a}^{+}$ ions occupy all eight tetrahedrall voids of the unit cell.
• D. $S^{2-}$ ions from $fcc$ lattice and $Z{n}^{2+}$ ions go into alternate tetrahedral voids of the unit cell.

Answer 1

Answer: (A), (D)

$S^{2-}$ ions from $fcc$ lattice and $Z{n}^{2+}$ ions go into alternate tetrahedral voids of the unit cell.
$C{l}^{-}$ ions from $fcc$ lattice and $N{a}^{+}$ ions occupy all octahedral voids of the unit cell.

The ratio of coordination number of ${Na}^{+}$ and ${Cl}^{-}$ in $\text{NaCl}$ is $1:1$ i.e. same coordination no. for both $N{a}^{+}$ and ${Cl}^{-}$.

The ratio of coordination number of ${Ca}^{+2}$ and $F^{-}$ in ${\text{CaF}}_2$ is $2:1$ i.e. different coordination no. for $C{a}^{+2}$ and $F^{-}$.

The ratio of coordination number of ${Na}^{+}$ and $O^{-2}$ in ${\text{Na}}_2\text{O}$ is $1:2$ i.e. different coordination no. for $N{a}^{+}$ and $O^{-2}$.

The ratio of coordination number of ${Zn}^{+2}$ and $S^{-2}$ in $\text{ZnS}$ is $1:1$ i.e. same coordination no. for both $Z{n}^{+2}$ and $S^{-2}$.

Hence, Options "A" & "D" are correct answers.