Which of the following sulphides has maximum solubility in water?

Options

A. CdS`(K_(sp) = 36 xx 10^(-30))`
B. FeS`(K_(sp) = 11 xx 10^(-20))`
C. HgS `(K_(sp) = 36 xx 10^(-54))`
D. ZnS`(K_(sp) = 11 xx 10^(-22)) `

Answer

To determine which of the following sulfides has the maximum solubility in water among CdS, FeS, HgS, and ZnS, we can follow these steps:

### Step 1: Understand the Dissociation of Sulfides
Each sulfide dissociates in water to form its respective ions. The general dissociation can be represented as:
- CdS → Cd²⁺ + S²⁻
- FeS → Fe²⁺ + S²⁻
- HgS → Hg²⁺ + S²⁻
- ZnS → Zn²⁺ + S²⁻

### Step 2: Write the Solubility Product Expression (Ksp)
The solubility product constant (Ksp) for each sulfide can be expressed as:
- For CdS: Ksp = [Cd²⁺][S²⁻]
- For FeS: Ksp = [Fe²⁺][S²⁻]
- For HgS: Ksp = [Hg²⁺][S²⁻]
- For ZnS: Ksp = [Zn²⁺][S²⁻]

### Step 3: Relate Solubility to Ksp
The solubility (S) of each sulfide can be related to Ksp:
- For CdS: S² = Ksp
- For FeS: S² = Ksp
- For HgS: S² = Ksp
- For ZnS: S² = Ksp

Thus, S = √Ksp.

### Step 4: Compare Ksp Values
To find out which sulfide has the maximum solubility, we need to compare the Ksp values of each sulfide:
- Ksp of FeS = 11 × 10⁻²⁰ (highest among the given options)
- Ksp of CdS, HgS, and ZnS are lower than that of FeS.

### Step 5: Conclusion
Since FeS has the highest Ksp value, it will have the maximum solubility in water among the given sulfides.

### Final Answer
The sulfide with maximum solubility in water is **FeS**.

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