On addition of aqueous $NaOH$ to a salt solution,a white gelatinous precipitate is formed,which dissolves in excess alkali. The salt solution contains

Identify the correct reactions and observations from the following:
$(1) \ NH_4^+ \xrightarrow[K_2HgI_4]{KOH} \text{ Brown ppt. (Nessler's reagent)}$
$(2) \ Ni^{2+} \xrightarrow{dmg/OH^-} \text{ Rosy red ppt.}$
$(3) \ FeCl_3(aq.) \xrightarrow{NH_4OH} \text{ Reddish brown ppt.}$
$(4) \ CuSO_4(aq.) \xrightarrow{\text{excess } NH_4OH} \text{ Deep blue solution}$

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

When calomel reacts with a solution of $NH_4OH$,which compound is formed?

When $H_2S$ is passed through a mixture containing $Cu^{2+}$,$Ni^{2+}$,and $Zn^{2+}$ in an acidic solution,which ion will precipitate?

The reagent used in the qualitative analysis of the $IV^{th}$ group basic radicals is: