### Step-by-Step Solution:
1. **Identify the Assertion and Reason**:
- **Assertion (A)**: Three states of matter are the result of balance between intermolecular forces and thermal energy of the molecules.
- **Reason (R)**: Intermolecular forces tend to keep the molecules together but thermal energy of molecules tends to keep them apart.
2. **Define the Three States of Matter**:
- The three states of matter are **solid**, **liquid**, and **gas**.
3. **Explain Intermolecular Forces**:
- Intermolecular forces are the forces that act between molecules. They play a crucial role in determining the physical properties of substances.
- In solids, these forces are very strong, which keeps the molecules closely packed in a fixed structure.
- In liquids, the intermolecular forces are moderate, allowing molecules to be close but not in a fixed position.
- In gases, the intermolecular forces are weak, allowing molecules to move freely and be far apart.
4. **Explain Thermal Energy**:
- Thermal energy refers to the energy that molecules possess due to their motion. It increases with temperature.
- In solids, thermal energy is low, resulting in limited molecular movement and a rigid structure.
- In liquids, thermal energy is moderate, allowing for some movement while still maintaining a close arrangement.
- In gases, thermal energy is high, resulting in rapid movement and molecules being far apart.
5. **Analyze the Balance**:
- The states of matter depend on the balance between intermolecular forces and thermal energy.
- In solids, strong intermolecular forces dominate over low thermal energy, resulting in a fixed structure.
- In liquids, intermolecular forces and thermal energy are balanced, allowing for fluidity while maintaining some structure.
- In gases, weak intermolecular forces are overcome by high thermal energy, leading to a dispersed arrangement.
6. **Evaluate the Assertion and Reason**:
- The assertion (A) is true because the three states of matter indeed result from the balance between intermolecular forces and thermal energy.
- The reason (R) is also true as it accurately describes the role of intermolecular forces in keeping molecules together and thermal energy in keeping them apart.
7. **Conclusion**:
- Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the correct answer is that both assertion and reason are true, and the reason is the correct explanation of the assertion.
