Which of the following ions gives a white precipitate when $HCl$ is added to its aqueous solution?

The $V^{-}A$ group precipitate was dissolved in $HNO_3$ and treated with an excess of $NH_4OH$. It gives a white precipitate because of:

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Fe(OH)_3 \downarrow + NaOH(\text{excess}) \longrightarrow \text{No reaction}$

The only cations present in a slightly acidic solution are $Fe^{3+}$,$Zn^{2+}$,and $Cu^{2+}$. The reagent that when added in excess to this solution would identify and separate $Fe^{3+}$ in one step is

$A$ solution prepared in conc. $HCl$ sometimes gives white turbidity even in the absence of $1^{st}$ group,when water is added to it. It is due to the presence of

An inorganic compound $X$ on treatment with concentrated $H_{2}SO_{4}$ produces brown fumes and gives a dark brown ring with $FeSO_{4}$ in the presence of concentrated $H_{2}SO_{4}$. Also,compound $X$ gives a precipitate $Y$ when its solution in dilute $HCl$ is treated with $H_{2}S$ gas. The precipitate $Y$ on treatment with concentrated $HNO_{3}$ followed by excess of $NH_{4}OH$ further gives a deep blue coloured solution. Compound $X$ is: