The term "fluid" typically refers to a substance that can flow and take the shape of its container. In physics, fluids encompass both liquids and gases. Therefore, the most accurate interpretation from your provided options is:
- It can flow freely.
While it is true that fluids do not have a fixed shape and can flow, they can be either liquid or gas, and they do have properties related to particle arrangement and volume. However, saying "it must be liquid" is not correct since gases are also classified as fluids. Similarly, the statement about not having a fixed volume applies more specifically to gases, as liquids have a fixed volume but can still be defined as fluids.