Question:
Consider the sulphides $\mathrm{HgS}, \mathrm{PbS}, \mathrm{CuS}, \mathrm{Sb}_{2} \mathrm{~S}_{3}$, $\mathrm{As}_{2} \mathrm{~S}_{3}$ and $\mathrm{CdS}$. Number of these sulphides soluble in $50 \% \mathrm{HNO}_{3}$ is
Solution:
$\mathrm{Pbs}, \mathrm{CuS}, \mathrm{As}_{2} \mathrm{~S}_{3}, \mathrm{CdS}$ are soluble in $50 \% \mathrm{HNO}_{3}$
$\mathrm{HgS}, \mathrm{Sb}_{2} \mathrm{~S}_{3}$ are insoluble in $50 \% \mathrm{HNO}_{3}$
So Answer is 4 .