Which of the following is least soluble ?

Options

A. `NiS(K_(sp)=3xx10^(-21))`
B. `FeS(K_(sp)=4xx10^(-19))`
C. `MnS(K_(sp)=7xx10^(-16))`
D. `PtS(K_(sp)=8xx10^(-73))`

Answer

To determine which of the given metal sulfides is least soluble, we need to compare their solubility product constants (Ksp values). The metal sulfides provided are NiS, FeS, MnS, and PtS.

### Step-by-Step Solution:

1. **Understanding Solubility Product (Ksp):**
- The solubility product constant (Ksp) is a measure of the solubility of a compound in water. A lower Ksp value indicates that the compound is less soluble.

2. **Identifying the Ksp Values:**
- We are given that:
- Ksp(NiS) < 10^-19
- Ksp(PtS) = 8 x 10^-73
- Ksp(FeS) and Ksp(MnS) values are not provided, but we can infer that they are higher than that of PtS based on the context.

3. **Comparing Ksp Values:**
- Since Ksp(PtS) = 8 x 10^-73 is significantly lower than Ksp(NiS) (which is less than 10^-19), we can conclude that PtS is the least soluble among the given options.

4. **Conclusion:**
- Therefore, the metal sulfide that is least soluble is **PtS**.

### Final Answer:
- The least soluble metal sulfide is **PtS (Option D)**.