Identification of Black Colored Metallic Sulfides

To determine the total number of sulfides that are black in colour, let us examine the characteristic colours of the precipitates for each given metal sulfide:

1. $\text{PbS}$ (Lead(II) sulfide): Black
2. $\text{CuS}$ (Copper(II) sulfide): Black
3. $\text{HgS}$ (Mercury(II) sulfide): Black (precipitated form as $\beta\text{-HgS}$ / metacinnabar)
4. $\text{MnS}$ (Manganese(II) sulfide): Buff / Salmon-pink / Flesh-coloured
5. $\text{Ag}_2\text{S}$ (Silver(I) sulfide): Black
6. $\text{NiS}$ (Nickel(II) sulfide): Black
7. $\text{CoS}$ (Cobalt(II) sulfide): Black
8. $\text{Bi}_2\text{S}_3$ (Bismuth(III) sulfide): Dark brown to Black (often classified as brownish-black or black)
9. $\text{SnS}_2$ (Tin(IV) sulfide): Yellow

Counting the black sulfides:

• Definitely black: $\text{PbS}$, $\text{CuS}$, $\text{HgS}$, $\text{Ag}_2\text{S}$, $\text{NiS}$, $\text{CoS}$ (6 sulfides)
• Including $\text{Bi}_2\text{S}_3$ (which is brownish-black/black): 7 sulfides

Thus, the total number of black-coloured sulfides is 6 (or 7 if $\text{Bi}_2\text{S}_3$ is counted as black).