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

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

In the group $III$ radicals,in place of $NH_4Cl$,which of the following can be used?

Match the List-$I$ with List-$II$ :

Cations	Group reaction
$P \rightarrow Pb^{2+}, Cu^{2+}$	$(i)$ $H_2S$ gas in presence of dilute $HCl$
$Q \rightarrow Al^{3+}, Fe^{3+}$	$(ii)$ $(NH_4)_2CO_3$ in presence of $NH_4OH$
$R \rightarrow Co^{2+}, Ni^{2+}$	$(iii)$ $NH_4OH$ in presence of $NH_4Cl$
$S \rightarrow Ba^{2+}, Ca^{2+}$	$(iv)$ $H_2S$ in presence of $NH_4OH$

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 ion will not be precipitated by aqueous $(NH_4)_2S$?