1. Indefinite shape and volume: Gases take the shape and volume of their container. They expand to fill the entire available space.

2. Low density: Gases have much lower densities than liquids or solids. This is because the particles are spread far apart.

3. High compressibility: Gases can be compressed easily, meaning their volume can be reduced by applying pressure.

4. Free movement of particles: Gas particles move randomly and rapidly in all directions. This constant motion is what gives gases their ability to fill containers.

5. Weak intermolecular forces: The attractive forces between gas molecules are very weak. This allows them to move freely and independently.