Aluminium when exposed to `O_(2)` atmosphere, formation of `Al_(2),O_(3)`, is observed. It is.

Options

A. corrosion
B. rusting
C. decomposition
D. rancidity

Explanation

### Step-by-Step Text Solution:

1. **Understanding the Reaction**:
When aluminum (Al) is exposed to oxygen (O₂), it reacts to form aluminum oxide (Al₂O₃). The balanced chemical equation for this reaction is:
\[ 4 \text{Al} + 3 \text{O}_2 \rightarrow 2 \text{Al}_2\text{O}_3 \]

2. **Formation of Protective Layer**:
The aluminum oxide (Al₂O₃) forms a thin layer on the surface of aluminum. This layer is protective in nature and prevents further oxidation of the underlying aluminum metal.

3. **Properties of Aluminum Oxide**:
The aluminum oxide layer is less shiny compared to pure aluminum. This is why aluminum utensils appear duller than the shiny aluminum metal itself.

4. **Definition of Corrosion**:
The process of a metal reacting with oxygen to form its oxide is known as corrosion. In this case, aluminum undergoing oxidation to form aluminum oxide is a clear example of corrosion.

5. **Benefits of the Corrosion Layer**:
The formation of the Al₂O₃ layer is beneficial because it protects the aluminum from further corrosion. It prevents the aluminum from reacting with moisture and other substances, which could lead to deterioration.

6. **Health Implications**:
If aluminum were to dissolve in food (which could happen if the protective layer were not present), it could pose health risks. The Al₂O₃ layer ensures that aluminum does not leach into food, making it safer for cooking.

7. **Conclusion**:
Therefore, the process of aluminum reacting with oxygen to form aluminum oxide is classified as corrosion. The correct answer to the question is option 1: Corrosion.