Question

A solid $XY$ has $NaCl$ structure. If radius of $X^{+}$is $100pm$, what is the radius of $Y^{-}$ ion?

• A. 120 pm
• B. 136.6 to 241.6 pm
• C. 136.6 pm
• D. 241.6 pm

Answer 1

Answer: (B)

For $NaCl$ type crystal
$\frac{r_{+}}{r_{-}}=0.414$ to $0.732$
$r_{-}=\underset{\text{(max)}}{\frac{r_{+}}{0.414}}$ or $\underset{\text{(min)}}{\frac{r_{+}}{0.732}}$
$=\frac{100}{0.414}$ to $\frac{100}{0.732}$
$=241.54$ to $136.6pm$