Which of the following reagents can be used for making the
distinction between `AgCl` and `AgI` ?

Options

A. Sodium thiosulphate solution
B. Dilute ammonia solution
C. Potassium cyanide solution
D. Dilute `HNO_(3)`

Explanation

To distinguish between AgCl (silver chloride) and AgI (silver iodide), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reagents**: We need to determine which reagents can differentiate between AgCl and AgI. The options provided are sodium thiosulfate, dilute ammonia, potassium cyanide, and dilute HNO3.

2. **Reaction with Sodium Thiosulfate**:
- When AgCl reacts with sodium thiosulfate (Na2S2O3), it forms a soluble complex:
\[ 3 \text{AgCl} + \text{Na}_2\text{S}_2\text{O}_3 \rightarrow \text{Na}_3[\text{AgS}_2\text{O}_3] + 2 \text{NaCl} \]
- When AgI reacts with sodium thiosulfate, it also forms a similar soluble complex:
\[ \text{AgI} + \text{Na}_2\text{S}_2\text{O}_3 \rightarrow \text{NaI} + \text{Na}_3[\text{AgS}_2\text{O}_3] \]
- **Conclusion**: Both AgCl and AgI form soluble complexes with sodium thiosulfate, so this reagent cannot distinguish between them.

3. **Reaction with Dilute Ammonia**:
- When AgCl is treated with dilute ammonia, it forms a soluble complex:
\[ \text{AgCl} + 2 \text{NH}_3 \rightarrow [\text{Ag(NH}_3)_2]^+ + \text{Cl}^- \]
- However, AgI does not dissolve in dilute ammonia and remains insoluble.
- **Conclusion**: This allows us to distinguish between AgCl (which dissolves) and AgI (which does not).

4. **Reaction with Potassium Cyanide**:
- Both AgCl and AgI react with potassium cyanide (KCN) to form soluble complexes:
\[ \text{AgCl} + 2 \text{CN}^- \rightarrow [\text{Ag(CN)}_2]^- \]
\[ \text{AgI} + 2 \text{CN}^- \rightarrow [\text{Ag(CN)}_2]^- \]
- **Conclusion**: This reagent cannot distinguish between AgCl and AgI as both are soluble.

5. **Reaction with Dilute HNO3**:
- Both AgCl and AgI are insoluble in dilute HNO3, leading to no reaction.
- **Conclusion**: This reagent also cannot distinguish between them.

### Final Conclusion:
The reagent that can be used to distinguish between AgCl and AgI is **dilute ammonia**, as it dissolves AgCl but not AgI.