The compound that is white in color is

Which one of the following statements is correct?

Addition of sodium thiosulphate solution to a solution of silver nitrate gives $X$ as a white precipitate, which is insoluble in water but soluble in excess thiosulphate solution to give $Y$. On boiling in water, $Y$ gives $Z$. $X$, $Y$, and $Z$ respectively are:

Which compound is used to distinguish between $Fe^{2+}$ and $Fe^{3+}$ ions?

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

The group reagent $NH_4Cl_{(s)}$ and aqueous $NH_3$ will precipitate which of the following ions?