Which one of the following shows the highest solubility in hot concentrated aqueous NaOH ?
(a)$\mathrm{La}(\mathrm{OH})_{3}$
(b)$\mathrm{Nd}(\mathrm{OH})_{3}$
(c)$\mathrm{Sm}(\mathrm{OH})_{3}$
(d)$\mathrm{Lu}(\mathrm{OH})_{3}$.
Answer
Answer: D ✓ checked by 4AB · confidence high
Explanation
The lanthanide hydroxides become less basic and more amphoteric with decreasing ionic radius; Lu(OH)₃, the smallest, dissolves in hot concentrated NaOH.