Which one of the following processes involve chemical reactions?

Options

A. Storing of oxygen gas under pressure in a gas cylinder
B. Liquefaction of air
C. Keeping petrol in a China dish in the open
D. Heating copper wire in the presence of air at high temperature

Explanation

To determine which of the given processes involves a chemical reaction, we need to understand the characteristics of a chemical reaction. A chemical reaction occurs when two or more substances (reactants) combine to form new substances (products) that have different properties from the reactants.

Let's analyze each option step by step:

1. **Storage of oxygen gas under pressure in a gas cylinder**:
- This process involves simply storing oxygen gas. There is no combination of substances or formation of new products.
- **Conclusion**: This is not a chemical reaction.

2. **Liquefaction of air**:
- This process involves changing the state of air from gas to liquid. It is a physical change, not a chemical change, as no new substances are formed.
- **Conclusion**: This is not a chemical reaction.

3. **Keeping petrol in a china dish and open**:
- In this scenario, petrol is simply placed in a dish. There is no reaction occurring, and no new products are formed.
- **Conclusion**: This is not a chemical reaction.

4. **Heating copper wire in the presence of air at high temperature**:
- When copper wire is heated in the presence of air, it reacts with oxygen to form copper oxide (CuO). This is a chemical reaction because new substances are formed, and the properties of copper oxide are different from those of copper and oxygen.
- **Conclusion**: This is a chemical reaction.

Based on the analysis above, the process that involves a chemical reaction is:

**Answer**: Heating copper wire in the presence of air at high temperature (Option 4).

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