Which of the following is not precipitated as sulphide by passing $H_2S$ in the presence of concentrated $HCl$?

An aqueous solution of a mixture of two inorganic salts,when treated with dilute $HCl$,gave a precipitate $(P)$ and a filtrate $(Q)$. The precipitate $P$ was found to dissolve in hot water. The filtrate $(Q)$ remained unchanged when treated with $H_2S$ in a dilute mineral acid medium. However,it gave a precipitate $(R)$ with $H_2S$ in an ammoniacal medium. The precipitate $R$ gave a coloured solution $(S)$ when treated with $H_2O_2$ in an aqueous $NaOH$ medium.
$1.$ The precipitate $P$ contains
$(A)$ $Pb^{2+}$ $(B)$ $Hg_2^{2+}$ $(C)$ $Ag^{+}$ $(D)$ $Hg^{2+}$
$2.$ The coloured solution $S$ contains
$(A)$ $Fe_2(SO_4)_3$ $(B)$ $CuSO_4$ $(C)$ $ZnSO_4$ $(D)$ $Na_2CrO_4$

$Al^{3+}$,$Fe^{3+}$,$Zn^{2+}$,and $Ni^{2+}$ ions are present in an acidic solution. Excess of ammonium chloride $(NH_4Cl)$ solution is added followed by the addition of ammonium hydroxide $(NH_4OH)$ solution. The resulting precipitate will contain:

The pair$(s)$ of ions where $BOTH$ the ions are precipitated upon passing $H_2S$ gas in the presence of dilute $HCl$,is(are):
$(A) Ba^{2+}, Zn^{2+}$
$(B) Bi^{3+}, Fe^{3+}$
$(C) Cu^{2+}, Pb^{2+}$
$(D) Hg^{2+}, Bi^{3+}$

$MgSO_4$ on reaction with $NH_4OH$ and $Na_2HPO_4$ forms a white crystalline precipitate. What is its formula?

When sodium nitroprusside is added to an alkaline solution containing sulfide ions,a ........ is obtained.