Question

In chromium chloride $\left(CrC{l}_3\right),C{l}^{-}$ ions have cubic close packed arrangement and $C{r}^{3+}$ ions are present in the octahedral holes. The fraction of the total number of holes occupied is

• A. $\frac{1}{3}$
• B. $\frac{1}{6}$
• C. $\frac{1}{9}$
• D. $\frac{1}{12}$

Answer 1

Answer: (C)

In $CrC{l}_3$ for every, $3C{l}^{-}$ ions, there is one $C{r}^{3+}$ ion is present.
Thus, if there are $3C{l}^{-}$ ions are present in CCP.
Number of octahedral voids = 3, and tetrahedral voids = 6
Total voids = 3+6=9
As $1C{r}^{3+}$ ion is present in the octahedral void, therefore, fraction of holes occupied $=\frac{1}{9}$