Which observation demonstrates diffusion of a gas in a classroom?

• A. The scent gradually fills the room from the source.
• B. The scent stays localized near the release point.
• C. The scent sinks to the floor immediately.
• D. The air becomes completely silent.

Answer: (A)

Gas diffusion is the spread of gas molecules from areas of higher concentration to areas of lower concentration due to their random motion. In a classroom, when a scent is released, its molecules move through the air in all directions and gradually mix with the surrounding air. Over time, the smell becomes detectable in more and more places, so the scent fills the room. This observation matches diffusion because the scent distributes from the source throughout the space.

If the scent stayed right where it was released, diffusion wouldn’t be occurring much. If the scent immediately sank to the floor, that would involve density or convection effects rather than diffusion alone. And an air that becomes completely silent has no direct link to how the scent molecules spread.