Question

A mineral `MX_(2)` crystallizes in ccp of `M^(2+)` ions whereas `X^(-)` ions occupy the tetrahedral voids. The number of cations and anions per unit cell, the coordination number of cation and percent of tetrahedral voids occupied are :
A. `4, 8, 8, 100%`
B. `4, 8, 8, 50%`
C. `8, 4, 8, 50%`
D. `8, 4, 8, 100%`

Answer 1

Correct Answer - A
In ccp arrangement `M^(2+)` ion has four atoms per unit cell. For `MX_(2)` type salt, the number of `X^(-)` ions per unit cell is eight. Moreover, the number of tetrahedral voids per unit cell is also eight. This means that `X^(-)` ions occupy `100%` of tetrahedral voids. The salt `MX_(2)` is coordination number of cations is 8.