Any article of iron if left in open for some time, acquires a film of brownish substance (rust) having chemical formula ____

Options

A. `Fe_(3)O_(4)`
B. `Fe_(2)O_(3).xH_(2)O`
C. `FeO`
D. `Fe(OH)_(2)`

Explanation

To answer the question about the chemical formula of rust, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Rust Formation**:
- Rust is formed when iron reacts with moisture in the air. This moisture contains both water (H2O) and oxygen (O2).

2. **Chemical Reaction**:
- The chemical reaction that leads to rust formation can be represented as:
\[ \text{Iron (Fe)} + \text{Oxygen (O}_2\text{)} + \text{Water (H}_2\text{O)} \rightarrow \text{Rust} \]

3. **Identifying the Chemical Formula**:
- The chemical formula for rust is generally represented as:
\[ \text{Fe}_2\text{O}_3 \cdot x\text{H}_2\text{O} \]
- Here, \( \text{Fe}_2\text{O}_3 \) represents iron(III) oxide, and \( x\text{H}_2\text{O} \) indicates that rust can contain varying amounts of water, which can be represented by different values of \( x \).

4. **Final Answer**:
- Therefore, the chemical formula of rust is:
\[ \text{Fe}_2\text{O}_3 \cdot x\text{H}_2\text{O} \]