Which of these causes rusting of iron?

Options

A. Electroplating the metal surface
B. Painting the metal surface
C. Washing the metal surface
D. Oiling the metal surface

Answer

To determine which of the given options causes rusting of iron, we need to analyze each option in the context of what rusting is and the conditions that promote it.

### Step-by-Step Solution:

1. **Understanding Rusting of Iron:**
- Rusting is a chemical process where iron (Fe) reacts with moisture (water) and oxygen (from the air) to form iron oxide, commonly known as rust (Fe2O3·nH2O).
- The reaction involves the oxidation of iron, where Fe^2+ ions are oxidized to Fe^3+ ions in the presence of moisture and air.

2. **Analyzing the Options:**
- **Option 1: Electroplating the metal surface**
- Electroplating involves depositing a layer of metal onto the surface of iron using an electric current. This process protects the iron from exposure to moisture and air, thereby preventing rusting.
- **Conclusion:** This does not cause rusting.

- **Option 2: Painting the metal surface**
- Painting creates a protective layer over the metal surface, which prevents moisture and air from coming into contact with the iron. This also helps in preventing rusting.
- **Conclusion:** This does not cause rusting.

- **Option 3: Washing the metal surface**
- Washing the metal surface introduces moisture. Since rusting requires moisture and air, washing can lead to rusting if the iron is left wet or not dried properly.
- **Conclusion:** This can cause rusting.

- **Option 4: Oiling the metal surface**
- Oiling the surface creates a barrier that prevents moisture and air from reaching the iron. This is a common method to protect iron from rusting.
- **Conclusion:** This does not cause rusting.

3. **Final Answer:**
- Based on the analysis, **Option 3: Washing the metal surface** is the correct answer as it can lead to rusting of iron.