Ionic Equilibrium In Solution

The ionic radii of lanthanides follow a general trend where the ionic radii decrease as we move from left to right across the series.
- Ce has the largest ionic radius among the three due to its position and electronic configuration in the 4f series.
- Eu is next because of the effect of the 4f electron configuration, which leads to a smaller size compared to Ce .
- Tb has the smallest ionic radius due to its higher nuclear charge and effective nuclear charge acting on the electrons.
Therefore, the correct order of ionic radii is: