Question

Select the correct order of radii of the given ions:

• A. Yb\textsuperscript{3+} < Sm\textsuperscript{3+} < Dy\textsuperscript{3+} < Pr\textsuperscript{3+}
• B. Yb\textsuperscript{3+} < Dy\textsuperscript{3+} < Sm\textsuperscript{3+} < Pr\textsuperscript{3+}
• C. Pr\textsuperscript{3+} < Sm\textsuperscript{3+} < Dy\textsuperscript{3+} < Yb\textsuperscript{3+}
• D. Pr\textsuperscript{3+} < Sm\textsuperscript{3+} < Yb\textsuperscript{3+} < Dy\textsuperscript{3+}

Hint:

Lanthanide contraction: radii decrease from Pr\textsuperscript{3+} to Yb\textsuperscript{3+} due to ineffective shielding of 4f orbitals.

Answer 1

The Correct Option is B

This trend represents the lanthanide contraction — across the lanthanide series, ionic radii decrease with increasing atomic number due to poor shielding effect of 4f orbitals. Hence, Yb\textsuperscript{3+} has the smallest and Pr\textsuperscript{3+} the largest ionic radius.