Which of the following would best demonstrate diffusion of a gas in a classroom?

• A. Release a small amount of perfume and observe the scent spreading through the room.
• B. A burning candle in a closed room.
• C. Observe how a gas weighs less than air.
• D. Heat the room to mix gases.

Answer: (A)

Diffusion is the spreading of gas particles from a region of higher concentration to one of lower concentration due to their random motion. When you release a small amount of perfume, the concentration of perfume molecules is initially high near the source and gradually becomes lower as the molecules spread out in all directions. Because these molecules move randomly in the air, the scent travels through the room, making you notice it in different spots. That visible spread of odor is a direct demonstration of diffusion.

The other scenarios don’t show diffusion of a gas in the same way: a burning candle in a closed room involves combustion and changes in gas composition, not the random spreading of gas molecules from a region of high concentration; noticing that a gas weighs less than air relates to density rather than diffusion; and heating the room to mix gases relies more on convection (air movement driven by temperature differences) than on diffusion.