According to kinetic molecular model, in gases

Analysis

This question tests your understanding of the Kinetic Molecular Theory of Matter, which describes how particles behave in different states of matter (solids, liquids, and gases). We need to identify the specific behavior of gas molecules.

Concept Explanation

The Kinetic Molecular Theory states that matter is made up of tiny particles that are in constant motion. The state of matter depends on the energy of these particles and the strength of the forces holding them together:

• Solids: Particles are closely packed in a fixed, regular pattern. They vibrate about fixed positions because intermolecular forces are very strong. (This matches Option D).
• Liquids: Particles are close together but can slide past one another. They have more energy than solids but are still held together by moderate intermolecular forces. (This matches Option B).
• Gases: Particles have very high kinetic energy. They are far apart, move randomly at high speeds, and have negligible intermolecular forces. Because they move randomly and are not held together, they expand to fill the entire volume of any container they are placed in.

Step-by-Step Solution

1. Evaluate Option D: This describes a solid. The particles are packed in a regular pattern.
2. Evaluate Option C: This also describes a solid. The mention of "vibrating about fixed positions" is a classic characteristic of solid-state particles.
3. Evaluate Option B: This describes a liquid. Particles in liquids are closer together than in gases and often form temporary clusters.
4. Evaluate Option A: This describes a gas. Because gas molecules have high kinetic energy and weak intermolecular forces, they spread out as far as possible, filling all available space.

Conclusion

Based on the kinetic molecular model, gases are characterized by large distances between molecules and their ability to expand to fill any container. Therefore, Option A is the correct description.

Exam Tip: When you see questions about states of matter, remember the "Energy vs. Order" rule:

• Solids = Low energy, High order (Fixed).
• Gases = High energy, Low order (Random/Spread out).