Thanks for the help if you can break down the steps during the answer since i am trying to see if i have solved this in the right way not copy :$)$

The average residence period for molecules of water in the first coordination sphere of an aquated trivalent lanthanoid ion is more comparable to that of an aquated s$-$block metal ion than to that of most aquated trivalent d$-$block metal ions.

Describe the term'residence time' in this context, and explain in full the roots of these observations.