Question

The radius of $La^{3+}$ (Atomic number of $La = 57$ ) is $1.06\mathring{A}$. Which one of the following given values will be closest to the radius of $Lu^{3+}$ (Atomic number of $Lu = 71$) ?

• A. $1.40\,\mathring{A}$
• B. $1.06\,\mathring{A}$
• C. $0.85\,\mathring{A}$
• D. $1.60\,\mathring{A}$

Answer 1

Answer: (C)

Ionic radii $\propto \frac{1}{z}$
Thus, $\frac{z_{2}}{z_{1}} \Rightarrow \frac{1.06}{\left(\text{Ionic radii of } Lu^{3+}\right)} = \frac{71}{57}$
$\Rightarrow $ Ionic radii of $Lu^{3+} = 0.85\,\mathring{A}$