The correct option is **C. Gases expand to fill their container and have no definite shape.** ### Detailed Explanation: 1. **Understanding the States of Matter**: - Matter exists in three primary states: solids, liquids, and gases. Each state has distinct characteristics based on the arrangement and behavior of its particles. 2. **Characteristics of Gases**: - **No Definite Shape**: Gases do not have a fixed shape. Instead, they take the shape of their container. This is because the particles in a gas are far apart and move freely, allowing them to spread out and fill any available space. - **Expansion**: Gases will expand to fill the entire volume of their container. This is due to the high kinetic energy of gas particles, which allows them to overcome intermolecular forces and move independently. - **Low Density**: Gases are generally less dense than solids and liquids because their particles are more spread out. This is a key characteristic that differentiates gases from the other states of matter. 3. **Why Option C is Correct**: - Option C accurately describes the behavior of gases. It highlights that gases expand to fill their container and lack a definite shape, which is a fundamental property of gases. ### Why the Other Options are Incorrect: - **Option A: Gases have a definite shape and volume.** - This statement is incorrect because gases do not have a definite shape or volume. Unlike solids, which maintain a fixed shape and volume, gases will conform to the shape of their container and can change volume based on pressure and temperature. - **Option B: Gases are incompressible and have a fixed volume.** - This option is also incorrect. Gases are compressible, meaning they can be compressed into a smaller volume when pressure is applied. Additionally, gases do not have a fixed volume; they will expand to fill the entire volume of their container. - **Option D: Gases are denser than both solids and liquids.** - This statement is false. Gases are typically much less dense than solids and liquids. The density of a substance is defined as its mass per unit volume. Since gas particles are much farther apart than those in solids and liquids, gases have lower densities. ### Common Pitfalls: - Students often confuse the properties of gases with those of liquids or solids. Remember that gases are unique in their ability to expand and fill their containers, while solids and liquids maintain a fixed shape and volume. - It’s important to remember that while gases can be compressed, liquids and solids cannot be compressed to the same extent due to their closely packed particles. ### Revision Summary: - Gases have no definite shape and expand to fill their container. - Gases are compressible and do not have a fixed volume. - Gases are generally less dense than solids and liquids. - Understanding the unique properties of gases is crucial for distinguishing them from solids and liquids.