When $MgSO_4$ is treated with $NH_4OH$ and $Na_2HPO_4$,a white crystalline solid is formed. What is its formula?

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 $NH_4OH$

Which ion is detected using Nessler's reagent?

$A$ mixture of two salts is used to prepare a solution $S$,which gives the following results:
White precipitate$(s)$ $\xleftarrow{\text{Dilute } NaOH(aq.) \text{ at Room temperature}}$ $S$ (aq. solution of the salts) $\xrightarrow{\text{Dilute } HCl(aq.) \text{ at Room temperature}}$ White precipitate$(s)$ only
The correct option$(s)$ for the salt mixture is(are):
$A$. $Pb(NO_3)_2$ and $Zn(NO_3)_2$
$B$. $Pb(NO_3)_2$ and $Bi(NO_3)_3$
$C$. $AgNO_3$ and $Bi(NO_3)_3$
$D$. $Pb(NO_3)_2$ and $Hg(NO_3)_2$

Aqueous solution of Mohr's salt gives the test of which ions?

Three separate samples of a solution of a single salt gave these test results: one formed a white precipitate with excess ammonia solution,one formed a white precipitate with dilute $NaCl$ solution,and one formed a black precipitate with $H_2S$. The salt could be: