Which of the following sets comprises chemical changes?

Options

A. Boiling of water, breaking of glass, rusting of iron.
B. Dissolving salt in water, digestion of food, shredding of paper.
C. Cooking of food, boiling of water, dissolving sugar in water.
D. Rusting of iron, burning of paper, digestion of food.

Answer

To determine which of the following sets comprises chemical changes, we first need to understand the definitions of physical and chemical changes.

### Step-by-Step Solution:

1. **Understanding Physical Change**:
- A physical change is a change in the appearance or state of a substance without altering its chemical composition.
- No new substances are formed during a physical change.

2. **Understanding Chemical Change**:
- A chemical change involves a change in the chemical composition of a substance.
- New substances are formed as a result of a chemical change.

3. **Analyzing the Options**:
- **Option 1: Boiling of Water**:
- When water is boiled, it changes from liquid to vapor. This is a change in state but does not involve a change in chemical composition. Therefore, it is a physical change.

- **Option 2: Breaking of Glass**:
- Breaking glass changes its shape and size but does not change its chemical composition. This is also a physical change.

- **Option 3: Rusting of Iron**:
- Rusting involves iron reacting with oxygen and moisture to form rust (iron oxide). This is a chemical change because a new substance is formed.

- **Option 4: Dissolving Salt in Water**:
- Dissolving salt in water results in a solution, but the chemical composition of salt (NaCl) remains unchanged. This is a physical change.

- **Option 5: Digestion of Food**:
- Digestion involves breaking down food into simpler molecules through chemical reactions. This is a chemical change.

- **Option 6: Shredding of Paper**:
- Shredding paper changes its size and shape but does not change its chemical composition. This is a physical change.

4. **Conclusion**:
- The only options that represent chemical changes are:
- Rusting of iron
- Digestion of food

Thus, the correct answer to the question is that the set comprising chemical changes includes "Rusting of Iron" and "Digestion of Food".