An aqueous solution contains the ions as $Hg_2^{2+}$,$Hg^{2+}$,$Pb^{2+}$,and $Cd^{2+}$. The addition of dilute $HCl$ $(6 \ N)$ precipitates:

Consider the following sequence of reactions:
$M^{2+}(aq.)$ $\xrightarrow{NH_4Cl(s) + (NH_4)_2CO_3 \, sol.} Q \downarrow$ $\xrightarrow[\text{Followed by addition of } (NH_4)_2C_2O_4]{CH_3COOH} R \downarrow$
Which of the following cations can form precipitate $Q$ but does not form precipitate $R$?

Assign $A, B, C, D$ from the given type of reaction:
$2KCN + Pb(NO_3)_2 \longrightarrow Pb(CN)_2 \downarrow + 2KNO_3$

Find the compound $A$ from the following reaction sequences:
$A$ $\xrightarrow{\text{aqua-regia}} B$ $\xrightarrow[(2) CH_3COOH]{(1) KNO_2 \mid NH_4OH} \text{yellow ppt}$

$(T)$ imparts violet colour $\xrightarrow{compd.\,(U) + conc.\,H_2SO_4}$ $(V)$ Red gas $\xrightarrow{NaOH + AgNO_3}$ $(W)$ Red ppt. $\xrightarrow{NH_3\,soln.}$ $(X)$
$(W)$ Red ppt. $\xrightarrow{dil.\,HCl}$ $(Y)$ white ppt.
$(U)$ $\xrightarrow[\Delta]{NaOH}$ $(Z)$ gas (gives white fumes with $HCl$)?
$(T)$ sublimes on heating
Identify $(T)$ to $(Z).$

Passing $H_2S$ gas into a mixture of $Mn^{2+}$,$Ni^{2+}$,$Cu^{2+}$ and $Hg^{2+}$ ions in an acidified aqueous solution precipitates