A \( \mathrm{CuSO}_{4}+\mathrm{H}_{2} \mathrm{~S}=\mathrm{CuS}+\mathrm{H}_{2} \mathrm{SO}_{4} \) (কালো)
B \( \mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}+\mathrm{H}_{2} \mathrm{~S}=\mathrm{PbS}+2 \mathrm{HNO}_{3} \) (কালো)
C \( \mathrm{HgCl}_{2}+\mathrm{H}_{2} \mathrm{~S}=\mathrm{HgS}+2 \mathrm{HCl} \) (কালো)
D \( \begin{array}{c}\mathrm{CdCl}_{2}+\mathrm{H}_{2} \mathrm{~S}=\underset{\text { (কালো })}{\mathrm{CdS}}+2 \mathrm{HCl} \\ \text { }\end{array} \)