What is effusion in relation to gas behavior?

Effusion refers specifically to the process through which gas molecules escape from a container into a vacuum or another area through a small opening, typically one whose diameter is much smaller than the average distance between the gas molecules themselves. This escape is a result of the random motion of gas particles, which collide with the walls of the container and the opening, allowing some molecules to pass through.

The key aspect that differentiates effusion from other gas behaviors is the focus on the tiny opening through which the gas escapes, rather than on the movement, mixing, or absorption of gases. Unlike diffusion, which involves the mixing of gas with other gases, effusion only concerns the movement of gas particles out of an enclosed space, making option B the most accurate description of effusion.