Choose the correct pair regarding solubility

Options

A. `CuS lt MnS`
B. `CoS gt ZnS`
C. `CdS gt NiS`
D. `CuS gt ZnS`

Answer

To solve the question regarding the correct pair of solubility, we need to analyze the solubility product constants (Ksp) of the given compounds. The solubility of a compound is directly proportional to its Ksp value. Let's evaluate each pair step by step.

### Step-by-Step Solution:

1. **Evaluate Ksp for CuS and MnS:**
- Ksp of CuS = \(1 \times 10^{-36}\)
- Ksp of MnS = \(1 \times 10^{-11}\)
- Since \(Ksp_{MnS} > Ksp_{CuS}\), it follows that the solubility of MnS is greater than that of CuS.
- **Conclusion:** CuS < MnS (This statement is correct).

2. **Evaluate Ksp for CoS and ZnS:**
- Ksp of CoS = \(1 \times 10^{-22}\)
- Ksp of ZnS = \(1 \times 10^{-23}\)
- Since \(Ksp_{CoS} > Ksp_{ZnS}\), it follows that the solubility of CoS is greater than that of ZnS.
- **Conclusion:** CoS > ZnS (This statement is correct).

3. **Evaluate Ksp for CdS and NiS:**
- Ksp of CdS = \(1 \times 10^{-28}\)
- Ksp of NiS = \(1 \times 10^{-22}\)
- Since \(Ksp_{NiS} > Ksp_{CdS}\), it follows that the solubility of NiS is greater than that of CdS.
- **Conclusion:** CdS < NiS (The statement given as CdS > NiS is incorrect).

4. **Evaluate Ksp for CuS and ZnS:**
- Ksp of CuS = \(1 \times 10^{-36}\)
- Ksp of ZnS = \(1 \times 10^{-23}\)
- Since \(Ksp_{ZnS} > Ksp_{CuS}\), it follows that the solubility of ZnS is greater than that of CuS.
- **Conclusion:** CuS < ZnS (The statement given as CuS > ZnS is incorrect).

### Final Answer:
The correct pairs regarding solubility are:
- A: CuS < MnS (Correct)
- B: CoS > ZnS (Correct)
- C: CdS < NiS (Incorrect)
- D: CuS < ZnS (Incorrect)

Thus, the correct pairs are A and B.