Expansion during heating

Options

A. occurs only in a solid
B. increases the density of the material
C. decreases the density of the material
D. occurs at the same rate for all liquids and solids.

Explanation

### Step-by-Step Solution:

1. **Understanding Thermal Expansion**:
- When a material is heated, it undergoes thermal expansion, meaning it increases in size. This can be visualized by considering a rod that expands when heated.

2. **Atoms in the Material**:
- The number of atoms in the material does not change during thermal expansion. The atoms remain the same in quantity before and after heating.

3. **Change in Arrangement of Atoms**:
- Although the number of atoms remains constant, their arrangement changes. In the unheated state, atoms are closely packed together. Upon heating, these atoms move apart from each other.

4. **Effect on Density**:
- Density is defined as mass per unit volume (Density = Mass/Volume). Since the mass of the material remains constant (the number of atoms does not change), but the volume increases due to thermal expansion, the density must decrease.

5. **Conclusion**:
- Therefore, when a material is heated and expands, the density of the material decreases.

### Final Answer:
The density of the material decreases during thermal expansion when heated.

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