Which sulphide is soluble in $(NH_4)_2CO_3$?

$A$ precipitate of which of the following is obtained when $HCl$ is added to a solution of stannous sulphide $(SnS)$ in yellow ammonium sulphide?

$A$ mixture of two salts is not water-soluble but dissolves completely in dilute hydrochloric acid to form a colourless solution. The mixture could be

Assign $A, B, C, D$ from the given type of reaction:
$2KCN + Pb(NO_3)_2 \longrightarrow Pb(CN)_2 \downarrow + 2KNO_3$

Find the compound $A$ from the following reaction sequences:
$A$ $\xrightarrow{\text{aqua-regia}} B$ $\xrightarrow[(2) CH_3COOH]{(1) KNO_2 \mid NH_4OH} \text{yellow ppt}$

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$(NH_4)_2SO_4 + Sr(OH)_2 \longrightarrow SrSO_4 \downarrow + 2NH_3 \uparrow + 2H_2O$