How can gases be best characterized?

Gases can best be characterized by the presence of molecules that are widely separated from each other, resulting in a significant amount of empty space between them. This vast distance allows gas molecules to move freely and rapidly in all directions, which is a defining feature of gases compared to other states of matter, such as solids and liquids.

In gases, the kinetic energy of the molecules is higher, facilitating their faster movement, which is also responsible for the ability of gases to fill the volume of their container completely. This behavior contrasts sharply with that of liquids and solids, where particles are either in close proximity or tightly structured, leading to different physical properties.

This characterization clarifies that gases do not possess the high density or structured particle arrangements seen in solids or the defined solute-solvent relationships characteristic of solutions. Instead, their unique combination of widely spaced molecules and rapid movement distinctly identifies them as gas.