$A$ solution contains $Cl^{-}$,$I^{-}$,and $SO_{4}^{2-}$ ions. Which of the following ions is capable of precipitating all of the above when added to this solution?

$Pb^{2+}$,$Cu^{2+}$,$Zn^{2+}$,and $Ni^{2+}$ ions are present in a given acidic solution. On passing hydrogen sulphide gas through this solution,the precipitate formed will contain:

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

$A$ white crystalline substance dissolves in water. On passing $H_2S$ in this solution,a black precipitate is obtained. The black precipitate dissolves completely in hot $HNO_3$. On adding a few drops of conc. $H_2SO_4$ a white precipitate is obtained. This precipitate is that of:

Consider the following reactions:
$X(aq.) \xrightarrow{K_4[Fe(CN)_6]}$ Chocolate brown ppt.
$X(aq.) \xrightarrow{AgNO_3}$ White ppt. (insoluble in dil. $HNO_3$)
Then $X$ will be:

Which of the following is sparingly soluble in cold water and fairly soluble in hot water?