Which of the following is a physical change?

Options

A. Burning of a candle
B. Clotting of blood
C. Evaporation of water
D. Digestion of food

Explanation

To determine which of the given options is a physical change, we need to analyze each option based on the characteristics of physical and chemical changes.

### Step-by-Step Solution:

1. **Understanding Physical vs. Chemical Change**:
- A **physical change** is a change that affects one or more physical properties of a substance. It is usually reversible and does not alter the chemical composition of the substance.
- A **chemical change**, on the other hand, involves a transformation that changes the chemical composition of a substance, resulting in the formation of new substances. This change is often irreversible.

2. **Analyzing the Options**:
- **Option A: Burning of Candle**:
- When a candle burns, it undergoes a chemical reaction (combustion) that produces new substances (like carbon dioxide and water vapor). Therefore, this is a chemical change.

- **Option B: Clotting of Blood**:
- Clotting of blood involves a series of biochemical reactions that lead to the formation of a clot. Once blood has clotted, it cannot be reverted back to its original form. Thus, this is also a chemical change.

- **Option C: Evaporation of Water**:
- Evaporation is the process where water changes from liquid to vapor. The chemical composition of water (H₂O) remains unchanged, and this process is reversible (water can be condensed back to liquid). Therefore, this is a physical change.

- **Option D: Digestion of Food**:
- Digestion involves breaking down food into simpler substances through chemical reactions. Once food is digested, it cannot be reverted back to its original form. Hence, this is a chemical change.

3. **Conclusion**:
- After analyzing all the options, it is clear that **Option C: Evaporation of Water** is the only physical change among the given choices.

### Final Answer:
**C. Evaporation of Water**