The colour of copper sulphide is

Consider the sulphides $HgS$,$PbS$,$CuS$,$Sb_{2}S_{3}$,$As_{2}S_{3}$ and $CdS$. Number of these sulphides soluble in $50\% \ HNO_{3}$ is .... .

$A$ solution containing a group $IV$ cation gives a precipitate on passing $H_2S$ gas. $A$ solution of this precipitate in dilute $HCl$ produces a white precipitate with $NaOH$ solution and a bluish-white precipitate with basic potassium ferrocyanide. The cation is:

Nessler's reagent is

Which reagent is used in the qualitative analysis of Group $IV$ cations?

When $H_2S$ gas is passed through a hot acidic aqueous solution containing $Al^{3+}$,$Cu^{2+}$,$Pb^{2+}$ and $Ni^{2+}$,a precipitate is formed,which consists of