What characterizes the properties of gases regarding shape and volume?

Gases possess unique characteristics that differentiate them from solids and liquids. They do not have a fixed shape or a fixed volume, allowing them to expand and fill the container they are in. This is due to the nature of gas particles, which are widely spaced apart and move freely, leading to greater dispersion in space compared to solids or liquids.

When a gas is contained within a vessel, the particles will spread out to occupy the entire volume, adjusting to the shape of the container. This property enables gases to take on various shapes depending on the container, and the volume is determined by the amount of gas present as well as external conditions such as pressure and temperature. The versatility in shape and volume is foundational to many applications involving gases, such as in the workings of engines, balloons, and various industrial processes.

In contrast, the other options suggest constraints that do not apply to gases: having a fixed shape or volume, or having a fixed shape but variable volume, which are characteristics of solids and liquids. Understanding these properties is essential for grasping concepts related to gas behavior and the gas laws.