Question

The arrangement of $X^{-}$ ions around $A^{+}$ ion in solid AX is given in the figure (not drawn to scale). If the radius of $X^{-}$ is 250 pm, the ideal radius of $A^{+}$ is

• A. 104 pm
• B. 183 pm
• C. 125 pm
• D. 57 pm

Answer 1

The correct option is A

104 pm

From figure,
$A^{\oplus }$ is present in the octahedral void of $X^{\ominus }$
For octahedral void,
$\frac{r{A}^{\oplus }}{r{X}^{\ominus }}=0.414$
$\Rightarrow r_{A^{\oplus }}=0.414\times r_{X^{\ominus }}=0.414\times 250pm\simeq 104pm$