Rusting on iron needs

Options

A. Dry air
B. Air and water
C. Distilled water and carbon dioxide
D. Oxygen and carbon dioxide

Answer

To determine what is needed for rusting on iron, we can break down the process step by step:

### Step 1: Identify the conditions necessary for rusting
Rusting is a chemical process that occurs when iron reacts with certain elements. The primary conditions necessary for rusting to occur are:

1. **Presence of Oxygen (O2)**: Rusting requires oxygen, which is typically found in the air.
2. **Presence of Water (H2O)**: Water is essential as it facilitates the electrochemical reactions that lead to rust formation.

### Step 2: Understand the chemical reaction involved
When iron (Fe) is exposed to both oxygen and water, it undergoes oxidation. The reaction can be summarized as follows:

- Iron reacts with oxygen in the presence of water to form hydrated iron oxide, commonly known as rust (Fe2O3·nH2O).

### Step 3: Analyze the options given in the question
The options provided are:
1. Dry air
2. Air and water
3. Distilled water and carbon dioxide
4. Oxygen and carbon dioxide

- **Option 1 (Dry air)**: This option is incorrect because dry air lacks the moisture (water) needed for rusting.
- **Option 2 (Air and water)**: This is the correct option, as both air (providing oxygen) and water are necessary for rusting to occur.
- **Option 3 (Distilled water and carbon dioxide)**: This option is incorrect because carbon dioxide does not play a role in the rusting process.
- **Option 4 (Oxygen and carbon dioxide)**: This option is also incorrect since carbon dioxide is not necessary for rusting.

### Conclusion
The correct answer is **Option 2: Air and water**. Rusting on iron needs both air (which contains oxygen) and water to occur.

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