The ion that can be precipitated by $HCl$ as well as $H_2S$ is

$X_2S_n + H_2O \to X(OH)_n \downarrow + Y \uparrow (Gas) \xrightarrow{Pb(CH_3COO)_2} Z \downarrow (Black \ ppt.)$
Then $(X)$ cation can not be

Which ion$(s)$ precipitate when an oxalate solution is added to a mixture of $Ba^{2+}$,$Sr^{2+}$,and $Ca^{2+}$?

$A$ 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

When $H_2S$ is passed through a solution in $Group-II$ analysis,it sometimes becomes milky. This indicates the presence of:

The compound that is white in color is