In which state of matter does a substance not have a definite shape or volume?

A substance that does not have a definite shape or volume is categorized as a gas. In this state of matter, particles are widely spaced and move independently, which allows gases to fill the entire volume of their container. The absence of a fixed shape means that gases will adapt to the shape of whatever space they occupy, and the lack of a definite volume indicates they can expand or be compressed depending on the external conditions, such as pressure and temperature.

Liquids, in contrast, have a definite volume but take the shape of their container. Solids maintain a fixed shape and volume because their particles are closely packed in a structured arrangement. Plasma, while also not having a definite shape or volume due to its high energy and the presence of free-moving ions and electrons, is a ionized state of matter distinct from gases. Thus, gases are the primary state characterized by the lack of both definite shape and volume.