How are the properties of gases typically described in terms of their physical states?

The correct choice highlights a key characteristic of gases in their physical state. Gases are distinguished by the lack of both a fixed shape and a fixed volume, which sets them apart from solids and liquids. Unlike solids, which maintain a consistent shape and volume, or liquids, which have a fixed volume but take the shape of their containers, gases expand to fill whatever space is available to them.

This behavior occurs because the molecules in a gas are in constant, rapid motion and are relatively far apart compared to those in solids or liquids. The intermolecular forces in gases are much weaker, allowing the gas particles to move freely and occupy any available volume. Consequently, when a gas is housed in a container, it will spread out evenly to fill the entire container regardless of its shape or size.

The other options misrepresent the nature of gases: they either attribute fixed volume or shape to gases, which contradicts their fundamental properties as described by the gas laws.