Which of the following involves only physical change ?

Options

A. Dissolution of lime in water.
B. Dissolution of carbon dioxide in water at high pressure.
C. Dissolution of concentrated acid in water.
D. Electrolysis of water.

Explanation

To determine which of the following involves only a physical change, we need to understand what constitutes a physical change versus a chemical change.

### Step-by-Step Solution:

1. **Understanding Physical Change**:
- A physical change is a change that affects one or more physical properties of a substance without altering its chemical composition. This means the substance remains the same at the molecular level, even though its form or state may change (e.g., solid to liquid).

2. **Identifying Examples**:
- Let's analyze the examples given in the transcript:
- **Dissolving lime (CaO) in water**: This results in the formation of calcium hydroxide (Ca(OH)₂), which is a new substance. Therefore, this is a **chemical change**.
- **Dissolving carbon dioxide (CO₂) in water**: This produces carbonic acid (H₂CO₃), which is also a new substance. Thus, this is a **chemical change**.
- **Dissolving concentrated acid in water**: When concentrated acid is mixed with water, it dilutes but does not form a new substance. The acid remains the same chemically, just in a different concentration. This is a **physical change**.
- **Electrolysis of water**: This process breaks water down into hydrogen and oxygen gases, resulting in new substances. Hence, this is a **chemical change**.

3. **Conclusion**:
- From the examples analyzed, the only process that involves only a physical change is the **dissolving of concentrated acid in water**.

### Final Answer:
The process that involves only a physical change is the **dissolving of concentrated acid in water**.

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