Question

Which one of the following metallic hydroxides does not dissolve in sodium hydroxide solution?

1. $Zn(OH{)}_2$

2. $Fe(OH{)}_3$

Answer 1

$Ans$ option 2

$Fe(OH{)}_3$ does not dissolve in $NaOH$ solution, because

it has low solubility constant of order ${10}^{-34}$ Hence it would not dissolve as

solubility constant $\alpha$ solubility

whereas $Zn(OH{)}_3$ generally exist in its complex,it is surrounded by water molecules. thus when $NaOH$ is added $O{H}^{-1}$ would reduce the complex and make it soluble hence it is soluble.