Which of the following is not considered a characteristic or property of a gas?

To understand why "particles" is not considered a distinct characteristic or property of a gas, it's important to clarify what properties define gases.

Gases are characterized by their lack of fixed shape and a tendency to expand to fill their container. The specific properties that are commonly used to describe gases include volume, mass, and pressure.

Volume refers to the amount of space that a gas occupies. Unlike solids and liquids, the volume of a gas can change depending on the container it is in. Mass is a measure of the amount of matter in a gas, indicating that gases possess weight. Pressure is the force exerted by gas particles colliding with the walls of their container, an essential factor in understanding gas behavior.

While particles (atoms or molecules) make up gases, the term itself does not define a property of gases but rather speaks to the composition of matter in all states (solid, liquid, and gas). Hence, it is not a characteristic unique to gases. Instead, it serves as a foundational concept in discussing matter as a whole, rather than a defining property that can be measured or observed in the same way that volume, mass, and pressure can be for gases specifically.