A black precipitate is obtained when H2S is passed through a dilute acidic (HCI) aqueous solution containing

Options

A. `Cu^(2+)` and`Pb^(2+)`
B. `Zn^(2+)`and `Mg^(2+)`
C. `Mg^(2+)` and `Fe^(3+)`
D. `Mg^(2+)`and `Ni^(2+)`

Answer

To solve the question regarding which ions will produce a black precipitate when H2S is passed through a dilute acidic (HCl) aqueous solution, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Ions Present**: The ions given in the question are Cu²⁺ (Copper), Pb²⁺ (Lead), Zn²⁺ (Zinc), Mg²⁺ (Magnesium), Fe³⁺ (Iron), and Ni²⁺ (Nickel).

2. **Understand the Reaction with H2S**: Hydrogen sulfide (H2S) is known to form precipitates with certain metal ions. The sulfides of some metals are insoluble in water and can precipitate out of solution.

3. **Analyze Each Ion**:
- **Zinc (Zn²⁺)**: Zinc sulfide (ZnS) is soluble in acidic solutions. Therefore, it will not form a precipitate in this case.
- **Iron (Fe³⁺)**: When H2S is passed through an acidic solution of Fe³⁺, it forms ferrous sulfide (FeS), which is not black but rather a greenish color. Thus, it does not yield a black precipitate.
- **Copper (Cu²⁺)**: Copper(II) sulfide (CuS) is insoluble and forms a black precipitate when H2S is passed through a solution containing Cu²⁺.
- **Lead (Pb²⁺)**: Lead(II) sulfide (PbS) is also insoluble and forms a black precipitate when H2S is passed through a solution containing Pb²⁺.
- **Magnesium (Mg²⁺)**: Magnesium sulfide (MgS) does not form a black precipitate in acidic conditions.
- **Nickel (Ni²⁺)**: Nickel sulfide (NiS) can form a precipitate, but it is not black; it is typically greenish or brownish.

4. **Conclusion**: The ions that produce a black precipitate when H2S is passed through a dilute acidic solution are Copper (Cu²⁺) and Lead (Pb²⁺).

5. **Final Answer**: The black precipitate is obtained from Copper (Cu²⁺) and Lead (Pb²⁺) ions.