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 compounds is the least soluble, we need to analyze the provided solubility product constants (Ksp) for each compound. The Ksp values indicate the solubility of the compounds in a saturated solution: a lower Ksp value corresponds to lower solubility.

### Step-by-Step Solution:

1. **Identify the Ksp Values**:
We have the following Ksp values for the compounds:
- NIS: \( Ksp = 3 \times 10^{-21} \)
- FES: \( Ksp = 4 \times 10^{-19} \)
- MNs: \( Ksp = 7 \times 10^{-16} \)
- PTS: \( Ksp = 8 \times 10^{-73} \)

2. **Compare the Ksp Values**:
We need to compare these Ksp values to determine which one is the smallest:
- \( 3 \times 10^{-21} \)
- \( 4 \times 10^{-19} \)
- \( 7 \times 10^{-16} \)
- \( 8 \times 10^{-73} \)

3. **Determine the Least Soluble Compound**:
The smallest Ksp value among these is \( 8 \times 10^{-73} \) (for PTS). Since Ksp is inversely related to solubility, the compound with the smallest Ksp value will be the least soluble.

4. **Conclusion**:
Therefore, the compound that is least soluble is **PTS**.

### Final Answer:
**PTS is the least soluble compound.**