Q29 / 160 · AP EAMCET 2023 (17 May Shift 1) · Chemistry

Select the correct order of radii of the given ions

  • A
    $\mathrm{Yb}^{3+} < \mathrm{Sm}^{3+} < \mathrm{Dy}^{3+} < \mathrm{Pr}^{3+}$
  • Correct answer
    B
    $\mathrm{Yb}^{3+} < \mathrm{Dy}^{3+} < \mathrm{Sm}^{3+} < \mathrm{Pr}^{3+}$
  • C
    $\mathrm{Pr}^{3+} < \mathrm{Sm}^{3+} < \mathrm{Dy}^{3+} < \mathrm{Yb}^{3+}$
  • D
    $\mathrm{Pr}^{3+} < \mathrm{Sm}^{3+} < \mathrm{Yb}^{3+} < \mathrm{Dy}^{3+}$

Solution

The correct order of ionic radii :- $\begin{aligned} & { }_{70} \mathrm{Yb}^{3+} < { }_{66} \mathrm{Dy}^{3+} < { }_{62} \mathrm{Sm}^{3+} < { }_{59} \mathrm{Pr}^{3+} \\ & (86 \mathrm{Pm}) \quad(91) \end{aligned}$ This order can be explained on the basis of lanthanide contraction due to which the atomic and ionic radii decrease steadily.

Hence, the correct answer is option: 'B'.

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