Question

Assertion :The ratio of $Z{n}^{2+}$ and $F^{-}$ per unit cell ZnS and $Ca{F}_2$ is 1:2. Reason: In ZnS, $Z{n}^{2+}$ ions occupy alternate tetrahedral voids and in $Ca{F}_2,F^{-}$ ions occupy all the tetrahedral voids of FCC unit cell.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

In $ZnS$ $Z{n}^{+2}\Rightarrow$ alternate tetrahedral void $⟶$ $\frac{1}{2}\times 8=4$ ions/unit cell

$S^{2-}\Rightarrow$ forms FCC lattice $⟶4$ ions/unit cell

In $Ca{F}_2$ $C{a}^{+2}\Rightarrow$ FCC lattice $⟶4$ ions/unit cell

$F^{-}\Rightarrow$ All tetrahedral voids $⟶8$ ions/unit cell

Ratio of $Z{n}^{+2}:F^{-}=4:8=1:2$