On saturating an aqueous solution of $Cu(II)$,$Pb(II)$,and $Zn(II)$ ions with $H_2S$,which of the following will precipitate?

Which of the following ions gives a white precipitate when $HCl$ is added to its aqueous solution?

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

$A$ 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.

The ion that can be precipitated by $HCl$ as well as $H_2S$ is

$Al^{3+}$,$Fe^{3+}$,$Zn^{2+}$,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: