Question

The radius of a divalent cation $A^{2+}$ is $94pm$ and that of a divalent anion $B^{2-}$ is $146pm$. The coordination number of $AB$ is:

• A. 4
• B. 6
• C. 8
• D. 3

Answer 1

The correct option is B 6

Radius ratio of ionic compounds helps in determining the coordination number and structure of compounds.
$\text{Radius of cation,}{r}^{+}=94pm$
$\text{Radius of anion,}{r}^{-}=146pm$
Radius ratio,
$\frac{r^{+}}{r^{-}}=\frac{94}{146}=0.64$
It is in the range of $0.414-0.732,$ which represent octahedral type of structure.
Thus, it has the coordination number of 6.