What is the full form of $DMG$?

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

Among $PbS$,$CuS$,$HgS$,$MnS$,$Ag_2S$,$NiS$,$CoS$,$Bi_2S_3$,and $SnS_2$,the total number of black coloured sulphides is

$Fe$ (finely powdered) $+ HCl(dil.) \to P + Q\uparrow$. Compound $P$ does not precipitate with:

$A$ colorless aqueous solution contains nitrates of two metals,$X$ and $Y$. When it was added to an aqueous solution of $NaCl$,a white precipitate was formed. This precipitate was found to be partly soluble in hot water to give a residue $P$ and a solution $Q$. The residue $P$ was soluble in aqueous $NH_3$ and also in excess sodium thiosulfate. The hot solution $Q$ gave a yellow precipitate with $KI$. The metals $X$ and $Y$,respectively,are

Which of the following sulfides is completely precipitated upon dilution of its acidic solution?