Question

Which statement describes effusion?
It occurs when a gas passes through a tiny hole.
It occurs when a liquid passes through a tiny hole.
It occurs when gas molecules disperse throughout a container.
It occurs when a liquid disperses throughout a container.

Answer 1

"It occurs when a gas passes through a tiny hole."

Effusion is the passage of gas molecules through a small orifice into a vacuum or lower-pressure region (Graham's law describes rates); diffusion is the spreading of gas throughout a container.