Question

Arrange the following ions in increasing order of ionic radii:
(A) Eu$^{3+}$
(B) Lu$^{3+}$
(C) Y$^{3+}$
(D) La$^{3+}$
Choose the correct answer from the options given below:

• A. A $<$ B $<$ C $<$ D
• B. A $<$ C $<$ B $<$ D
• C. B $<$ C $<$ A $<$ D
• D. C $<$ B $<$ D $<$ A

Answer 1

Answer: (D)

C $<$ B $<$ D $<$ A

Answer 2

The ionic radii generally increase down a group in the periodic table. However, for the
lanthanide series, there are some considerations:
1. $Y^{3+}$ : It has the smallest ionic radius among these ions due to its position in the periodic
table and the high effective nuclear charge.
2. $Lu^{3+}$ : Although it is at the end of the lanthanide series, the ionic radius is relatively
small due to the increase in nuclear charge.
3. $La^{3+}$ : This ion has a larger radius than Lu3+ and Y3+ because it is located above in the
lanthanide series.
4. $Eu^{3+}$ : This ion has the largest ionic radius among the listed ions.
Therefore, the correct increasing order of ionic radii is:

$Y^{3+} < Lu^{3+} < La^{3+} < Eu^{3+}$