Question

Of the following oxides, all are soluble in $NaOH\left(aq\right)$ except :

• A. $ZnO$
• B. ${Al}_2{O}_3$
• C. ${Fe}_2{O}_3$
• D. ${SnO}_2$

Answer 1

The correct option is C ${Fe}_2{O}_3$

$ZnO$, ${Al}_2{O}_3$ and ${SnO}_2$ are soluble in $NaOH\left(aq\right),$ as they form sodium zincate $N{a}_{2}Zn{O}_2$, sodium meta aluminate $Na\left[Al{O}_2\right]$ and sodium stannate $N{a}_{2}Sn{O}_2$ respectively. Whereas, ${Fe}_2{O}_3$ is insoluble in $NaOH\left(aq\right)$.