Question

Which one of the following shows the highest solubility in not conc. aqs. $NaOH$?

• A. $La(OH{)}_3$
• B. $Na(OH{)}_3$
• C. $Sm(OH{)}_3$
• D. $Lu(OH{)}_3$

Answer 1

Answer: (D)

$L{u}^{3+}$ is smallest in size, therefore $Lu(OH{)}_3$ complex most easily formed with $NaOH$ and dissolve.
$Lu(OH{)}_3+3O{H}^{-}\to [Lu(OH{)}_6{]}^{3-}$