Which of the following is not a chemical reaction?

Options

A. Souring of milk
B. Dissolution of sugar in water
C. Rusting of iron
D. Digestion of food in our body

Explanation

To determine which of the following options is not a chemical reaction, we need to analyze each option based on the definition of a chemical reaction. A chemical reaction is a process where one or more substances are transformed into new substances with different properties.

### Step-by-Step Solution:

1. **Identify the Options**: The options given are:
- a. Soaring of milk
- b. Dissolution of sugar in water
- c. Rusting of iron
- d. Digestion of food in our body

2. **Analyze Option A - Soaring of Milk**:
- Soaring of milk involves the process of curdling, where the proteins in milk change structure and form curds. This is a chemical change as new substances are formed.
- **Conclusion**: This is a chemical reaction.

3. **Analyze Option B - Dissolution of Sugar in Water**:
- When sugar dissolves in water, it does not form a new substance. The sugar molecules remain intact, and only their physical state changes. This is a physical change, not a chemical reaction.
- **Conclusion**: This is NOT a chemical reaction.

4. **Analyze Option C - Rusting of Iron**:
- Rusting is a process where iron reacts with oxygen and moisture to form rust (iron oxide). This involves a chemical change as new substances are formed.
- **Conclusion**: This is a chemical reaction.

5. **Analyze Option D - Digestion of Food in Our Body**:
- Digestion involves breaking down food into smaller molecules through various chemical processes. This results in new substances being formed, indicating a chemical change.
- **Conclusion**: This is a chemical reaction.

6. **Final Conclusion**:
- The only option that does not involve a chemical reaction is **b. Dissolution of sugar in water**.

### Answer:
The option that is not a chemical reaction is **b. Dissolution of sugar in water**.

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