Which of the following is not precipitate by `H_(2)S` in presence of cone acid soln

Options

A. `Cu^(2+)`
B. `Al^(3+)`
C. `Sb^(3+)`
D. `Cd^(2+)`

Answer

To determine which of the following ions is not precipitated by hydrogen sulfide (H₂S) in the presence of concentrated acid solution, we will analyze the solubility of various metal sulfides.

### Step-by-Step Solution:

1. **Understanding the Question**: We need to identify which metal ion does not form a precipitate when H₂S is added to a solution containing concentrated acid.

2. **Identify Common Metal Ions**: Common metal ions that are tested in qualitative analysis include:
- Lead (Pb²⁺)
- Cadmium (Cd²⁺)
- Copper (Cu²⁺)
- Nickel (Ni²⁺)
- Zinc (Zn²⁺)

3. **Behavior of Metal Ions with H₂S**: In the presence of H₂S, many metal ions form insoluble sulfides. However, the solubility of these sulfides can vary based on the concentration of the acid present.

4. **Focus on Cadmium Ion (Cd²⁺)**:
- Cadmium sulfide (CdS) is known to have a higher solubility product compared to other metal sulfides in group 2.
- This means that in concentrated acid solutions, cadmium ions do not precipitate as CdS because the conditions do not favor the formation of the insoluble sulfide.

5. **Dilution Requirement**:
- For cadmium sulfide to precipitate, the solution must be diluted before adding H₂S. This is due to the higher solubility product of CdS compared to other sulfides in group 2.

6. **Conclusion**:
- Therefore, the metal ion that is not precipitated by H₂S in the presence of concentrated acid solution is **Cadmium (Cd²⁺)**.

### Final Answer:
Cadmium ion (Cd²⁺) is not precipitated by H₂S in the presence of concentrated acid solution.

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