b
Copper sulphide is black in colour. $Cu^{2+}$ is placed in $II$ group of inorganic qualitative analysis. It is precipitated in the form of sulphide by passing $H_2S$ in presence of dil. $HCl$.
$C{{u}^{2+}}\,+\,{{H}_{2}}S\,\to \,\underset{\text{black}}{\mathop{CuS}}\,\,+\,2{{H}^{+}}$