This question tests your knowledge of the characteristic colors of metal sulfides, which is important in qualitative inorganic analysis (especially in group separation schemes). Many metal sulfides have distinct colors that help identify them.

Let's analyze each sulfide one by step:

Step 1: PbS (Lead sulfide) - Black

Step 2: CuS (Copper sulfide) - Black

Step 3: HgS (Mercury sulfide) - Black (in its metacinnabar form) or red (as cinnabar)

Step 4: MnS (Manganese sulfide) - Salmon pink (flesh-colored)

Step 5: Ag₂S (Silver sulfide) - Black

Step 6: NiS (Nickel sulfide) - Black

Step 7: CoS (Cobalt sulfide) - Black

Step 8: Bi₂S₃ (Bismuth sulfide) - Dark brown (often described as blackish-brown)

Step 9: SnS₂ (Tin sulfide) - Yellow

Final Count: The black colored sulfides are: PbS, CuS, HgS (considered black for analytical purposes), Ag₂S, NiS, CoS. Bi₂S₃ is dark brown but often grouped with black sulfides in analytical schemes. This gives us a total of 7 black sulfides.

Related Topics & Theory

Qualitative Analysis: This is a systematic method for identifying cations and anions in a salt mixture. Sulfides play a crucial role in the classic hydrogen sulfide (H₂S) scheme for cation analysis. Cations are grouped based on the solubility of their chlorides, sulfides, and carbonates.

Group IV Cations: This group includes Ni²⁺, Co²⁺, Mn²⁺, and Zn²⁺, which are precipitated as their sulfides in alkaline medium. Their colors are important for identification (e.g., ZnS is white, MnS is pink, NiS/CoS are black).

Group II Cations: This group is divided into IIA (Hg²⁺, Cu²⁺, Bi³⁺, Cd²⁺, Pb²⁺, Sn^2+/4+, As^3+/5+, Sb^3+/5+) whose sulfides are insoluble in yellow ammonium sulfide. Most of these sulfides are black or dark-colored.

Important Formulae & Colors

Memorizing the colors of common sulfides is key:

• Black: PbS, CuS, HgS, Ag₂S, NiS, CoS, FeS
• Yellow: CdS, SnS₂, As₂S₃
• Orange: Sb₂S₃
• White: ZnS
• Pink (Flesh-colored): MnS