What phrase best describes diffusion in gases?

Diffusion in gases is best described as the spreading of one gas into another gas. This process occurs due to the random motion of gas molecules as they collide and interact with one another. In a mixture of gases, the molecules move from an area of higher concentration to an area of lower concentration until equilibrium is achieved.

This phenomenon is a hallmark of gases, as their particles have significant kinetic energy and can move freely throughout a space. As a result, gases will mix uniformly when given enough time and allow for unrestricted movement.

Other concepts such as movement against pressure or separation by density relate to different physical principles, such as gas dynamics and buoyancy, rather than the fundamental process of diffusion itself.