Identify the correct order of solubility of `Na_(2)S, CuS` and ZnS in aqueous solution :

Options

A. `CuS gt ZnS gt Na_(2)S`
B. `ZnS gt Na_(2)S gt CuS`
C. `Na_(2)S gt CuS gt ZnS`
D. `Na_(2)S gt ZnS gt CuS`

Explanation

To determine the correct order of solubility of Na₂S, CuS, and ZnS in aqueous solution, we can follow these steps:

### Step 1: Understand the dissociation of each compound
- **Na₂S** dissociates into 2 Na⁺ ions and 1 S²⁻ ion. Therefore, it produces a total of 3 ions:
\[ \text{Na}_2\text{S} \rightarrow 2 \text{Na}^+ + \text{S}^{2-} \]

- **CuS** dissociates into 1 Cu²⁺ ion and 1 S²⁻ ion, resulting in a total of 2 ions:
\[ \text{CuS} \rightarrow \text{Cu}^{2+} + \text{S}^{2-} \]

- **ZnS** also dissociates into 1 Zn²⁺ ion and 1 S²⁻ ion, leading to a total of 2 ions:
\[ \text{ZnS} \rightarrow \text{Zn}^{2+} + \text{S}^{2-} \]

### Step 2: Compare the number of ions produced
The solubility of a salt in solution is generally higher when it produces more ions upon dissociation. Here:
- Na₂S produces 3 ions.
- CuS and ZnS each produce 2 ions.

Thus, Na₂S has the highest solubility due to the greater number of ions produced.

### Step 3: Compare the solubility of CuS and ZnS
Next, we need to compare the solubility of CuS and ZnS. This can be assessed using their solubility product constants (Ksp):
- **Ksp values**: Generally, the higher the Ksp, the more soluble the compound.
- Copper (Cu) belongs to group 2 in qualitative analysis, where the Ksp values tend to be lower.
- Zinc (Zn) belongs to group 4, where the Ksp values are generally higher.

Since ZnS has a higher Ksp than CuS, it is more soluble.

### Step 4: Final order of solubility
From the analysis:
1. Na₂S (highest solubility)
2. ZnS (higher solubility than CuS)
3. CuS (lowest solubility)

Thus, the correct order of solubility in aqueous solution is:
\[ \text{Na}_2\text{S} > \text{ZnS} > \text{CuS} \]

### Conclusion
The final answer is:
**Na₂S > ZnS > CuS**

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