In what order the reagents `Na_(2)S, NaCl and Nal` are added to an aqueous solution containing `Ag^(+), Cu^(+2) and Ni^(+2)` ions in order to precipitate `Ag^(+)` first `Cu^(+2)` second and `Ni^(+2)` last.

Options

A. `Na_(2)S, Nal, NaCl`
B. `NaCl, Na_(2)S, Nal`
C. `Nal, NaCl, Na_(2)S`
D. `NaCl, Nal, Na_(2)S`

Answer

To determine the order in which the reagents Na₂S, NaCl, and NaI should be added to an aqueous solution containing Ag⁺, Cu²⁺, and Ni²⁺ ions, we need to consider the solubility products (Ksp) of the respective precipitates formed with these reagents.

### Step-by-step Solution:

1. **Identify the ions and their precipitates**:
- Ag⁺ can form precipitates with Cl⁻ (AgCl), I⁻ (AgI), and S²⁻ (Ag₂S).
- Cu²⁺ can form precipitates with I⁻ (CuI), Cl⁻ (CuCl), and S²⁻ (CuS).
- Ni²⁺ can form precipitates primarily with S²⁻ (NiS).

2. **Determine the order of precipitation based on solubility**:
- **For Ag⁺**:
- AgCl is the least soluble among AgCl, AgI, and Ag₂S. Therefore, adding NaCl will precipitate Ag⁺ first.
- **For Cu²⁺**:
- CuI is less soluble than CuCl and CuS. Therefore, after Ag⁺ is precipitated, adding NaI will precipitate Cu²⁺ second.
- **For Ni²⁺**:
- Ni²⁺ only precipitates with S²⁻, and it is the least soluble. Thus, Na₂S should be added last to precipitate Ni²⁺.

3. **Final order of addition**:
- First: Add NaCl to precipitate Ag⁺ as AgCl.
- Second: Add NaI to precipitate Cu²⁺ as CuI.
- Last: Add Na₂S to precipitate Ni²⁺ as NiS.

### Conclusion:
The order of addition of the reagents to precipitate Ag⁺ first, Cu²⁺ second, and Ni²⁺ last is:
- **NaCl → NaI → Na₂S**