Which ion$(s)$ precipitate when an oxalate solution is added to a mixture of $Ba^{2+}$,$Sr^{2+}$,and $Ca^{2+}$?

Which of the following gives a black precipitate when $H_2S$ gas is passed through its solution?

$(T)$ 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 $(Z).$

$A$ laboratory reagent imparts green colour to the flame. On heating with solid $K_2Cr_2O_7$ and conc. $H_2SO_4$,it evolves a red gas. Identify the reagent.

If $Pb^{2+}, Cu^{2+}, Al^{3+}, Cd^{2+}, Zn^{2+}$ radicals are present in an aqueous solution,and it reacts with $H^{+}/H_2S$,a precipitate is produced. The solution $(X)$ obtained after the removal of the precipitate is treated with excess $NaOH$. What is the result?

In the group analysis of cations, $Ba^{2+}$ and $Ca^{2+}$ are precipitated respectively as