Why does `AgNO_(3)` produced a black stain on the skin?

Answer

To understand why `AgNO3` (silver nitrate) produces a black stain on the skin, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Understanding Silver Nitrate (AgNO3)**:
- Silver nitrate is a chemical compound that is sensitive to light and organic matter.

2. **Application on Skin**:
- When silver nitrate is applied to the skin, it interacts with the organic matter present in the skin.

3. **Decomposition Reaction**:
- Upon exposure to light, silver nitrate undergoes a decomposition reaction. This reaction can be represented as:
\[ 2 \, \text{AgNO}_3 \rightarrow 2 \, \text{Ag} + 2 \, \text{NO}_2 + \text{O}_2 \]
- In this reaction, silver nitrate decomposes to produce metallic silver (Ag), nitrogen dioxide (NO2), and oxygen gas (O2).

4. **Formation of Black Stain**:
- The metallic silver produced in the reaction is what causes the black stain on the skin. Metallic silver appears black, which is why the stain is observed.

5. **Conclusion**:
- Therefore, the black stain on the skin from `AgNO3` is due to the formation of metallic silver as a result of the decomposition of silver nitrate when it is exposed to light and organic matter.

### Summary:
The black stain produced by `AgNO3` on the skin is due to the formation of metallic silver from the decomposition of silver nitrate, which occurs when it interacts with light and organic matter.