Which of the following reagents is commonly used to detect the presence of sulfide ions?

In qualitative analysis,in order to detect $II$ group basic radicals,$H_2S$ gas is passed in the presence of dilute $HCl$ to:

Aqueous solution of $FeSO_4$ does not produce a precipitate with:

What precipitate is formed when $SnCl_2$ is added to $HgCl_2$?

Addition of $SnCl_2$ to $HgCl_2$ gives a precipitate of which color?

During the qualitative analysis of a salt with cation $y^{2+}$,the addition of a reagent $(X)$ to an alkaline solution of the salt gives a bright red precipitate. The reagent $(X)$ and the cation $(y^{2+})$ present are respectively .... .