**Correct Option: B. Particles in a solid are closely packed and vibrate in fixed positions.** ### Detailed Explanation: To understand the behavior of particles in solids compared to gases, we need to look at the arrangement and movement of particles in these two states of matter. 1. **Particle Arrangement:** - In solids, particles are closely packed together in a fixed, orderly arrangement. This close packing is due to strong intermolecular forces (like ionic, covalent, or metallic bonds) that hold the particles in place. Because of this arrangement, solids have a definite shape and volume. - In contrast, particles in a gas are much farther apart and are not arranged in any fixed pattern. The intermolecular forces in gases are very weak, allowing the particles to move freely and occupy any available space. 2. **Particle Motion:** - In solids, while the particles are closely packed, they are not stationary. Instead, they vibrate in place. This means that although they can move slightly, they cannot change their positions relative to one another. This vibration is due to thermal energy, which increases with temperature. - In gases, particles are in constant, rapid motion. They move in straight lines until they collide with either other gas particles or the walls of their container. This motion allows gases to fill the entire volume of their container, leading to no definite shape or volume. 3. **Intermolecular Forces:** - The strong intermolecular forces in solids keep the particles in fixed positions, which is why they maintain a definite shape. The energy of the particles is not enough to overcome these forces significantly, leading to their vibrational motion. - In gases, the weak intermolecular forces allow particles to move freely, which is why they can expand to fill any container. ### Why Other Options Are Incorrect: - **Option A: Particles in a solid are in constant motion and can easily change positions.** - This statement is misleading. While it is true that particles in a solid are in constant motion (vibrating), they cannot easily change positions due to the strong intermolecular forces that keep them in fixed locations. This option incorrectly implies that solids have the same level of mobility as gases. - **Option C: Particles in a gas are closely packed and vibrate in fixed positions.** - This statement is incorrect because it describes the behavior of particles in a solid, not a gas. In gases, particles are not closely packed; they are far apart and move freely without fixed positions. This is a fundamental difference between solids and gases. - **Option D: Particles in a solid have no interactions with each other.** - This statement is false. In solids, particles interact strongly with each other due to the strong intermolecular forces. These interactions are what keep the particles in fixed positions and give solids their structural integrity. ### Summary of Key Points: - **Solid Particles:** Closely packed, vibrate in fixed positions due to strong intermolecular forces. - **Gas Particles:** Far apart, move freely, and do not have a fixed arrangement or position. - **Intermolecular Forces:** Strong in solids, weak in gases, affecting particle behavior and arrangement. - **Motion:** Solids vibrate in place; gases are in constant, rapid motion. This understanding of particle behavior is crucial for grasping the fundamental differences between states of matter, which is a key concept in chemistry.