Which of the following sulphate has the lowest solubility product ?

Options

A. FeS
B. MnS
C. PbS
D. ZnS

Answer

To determine which of the given sulfides has the lowest solubility product (Ksp), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Compounds**: The sulfides provided in the question are:
- Iron sulfide (FeS)
- Manganese sulfide (MnS)
- Lead sulfide (PbS)
- Zinc sulfide (ZnS)

2. **Understand Solubility Product (Ksp)**: The solubility product (Ksp) is an equilibrium constant that applies to the dissolution of sparingly soluble salts. It is defined as the product of the molar concentrations of the ions, each raised to the power of their coefficients in the balanced equation.

3. **Group 2 Cations**: Group 2 cations (alkaline earth metals) generally form sulfides that are less soluble in water compared to other groups. Among the given sulfides, lead (Pb) is a Group 2 cation.

4. **Compare Solubility**:
- **FeS**: Iron sulfide is moderately soluble.
- **MnS**: Manganese sulfide is also moderately soluble.
- **PbS**: Lead sulfide is known to be very poorly soluble in water.
- **ZnS**: Zinc sulfide is also poorly soluble but not as much as lead sulfide.

5. **Conclusion**: Since lead sulfide (PbS) is the least soluble among the given sulfides, it will have the lowest solubility product (Ksp).

### Final Answer:
The sulfide with the lowest solubility product is **Lead sulfide (PbS)**.

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