$A$ black sulphide is formed by the action of $H_2S$ on

In the group $III$ radicals,in place of $NH_4Cl$,which of the following can be used?

What is formed when calomel $(Hg_2Cl_2)$ reacts with $NH_4OH$?

Which ion will form a precipitate with both $HCl$ and $H_2S$?

The reagents $NH_4Cl$ and aqueous $NH_3$ will precipitate which of the following ions?

$A$ is:
$\text{Salt } A \text{ (Colourless)} \xrightarrow{Cu} \text{Blue solution}$
$\text{Salt } A \text{ (Colourless)} \xrightarrow{HCl_{(aq)}} \text{White ppt}$
$\text{Salt } A \text{ (Colourless)} \xrightarrow{\text{Conc. } H_2SO_4} \text{Brown fumes}$