In scientific terms, what is used to refer to both liquids and gases?

In scientific terminology, the term that encompasses both liquids and gases is "fluids." This classification is based on the ability of both states of matter to flow and take the shape of their containers. Liquids have a definite volume but no definite shape, while gases have neither a definite volume nor a definite shape, expanding to fill the space available to them.

The concept of fluids is fundamental in various fields, including physics and engineering, where the behavior of liquids and gases under different conditions is studied. The term "fluids" highlights the shared characteristics of these two states, allowing for a unified understanding of their behavior in dynamic systems.

The other options, while related to matter, do not accurately refer to both liquids and gases. Particles may refer to the constituents of all states of matter, but it doesn’t specifically denote the flowing nature of liquids and gases. Solids, on the other hand, denote a distinct state of matter that does not have the same flowing properties. Atoms represent the basic building blocks of matter and do not specifically refer to the behavior or characteristics of either liquids or gases. Thus, "fluids" is the appropriate term that captures the essence of both liquids and gases in scientific discourse.