Question

The correct order of ionic radii of $Y ^{3+}, La ^{3+}, Eu ^{3+}$ and $Lu ^{3+}$ is (Atomic nos. $Y =39, La =57, Eu =63, Lu =71$ )

• A. $La ^{3+}< Eu ^{3+}< Lu ^{3+}< Y ^{3+}$
• B. $Y ^{3+}< La ^{3+}< Eu ^{3+}< Lu ^{3+}$
• C. $Y ^{3+}< Lu ^{3+}< Eu ^{3+}< La ^{3+}$
• D. $Lu ^{3+}< Eu ^{3+}< La ^{3+}< Y ^{3+}$

Answer 1

Answer: (C)

In lanthanide series there is a regular decrease in the atomic as well as ionic radii of trivalent ions $\left( M ^{3+}\right)$ as the atomic number increases. Although the atomic radii do show some irregularities but ionic radii decreases from La $(103 pm )$ to $Lu (86 pm ) . Y ^{3+}$ belong to second transition series therefore have greater ionic radii then other ions of third transition series.