Answer:
Diffusion
Step-by-step explanation:
When someone opens a lunch box, the molecules of the food inside it start to diffuse into the surrounding air. Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. In this case, the molecules of the food are at a higher concentration inside the lunch box, and when the box is opened, they start to spread out into the air where their concentration is lower.
As the molecules of the food move out of the lunch box and into the air, they collide with the air molecules, and this causes them to spread out even further. The movement of the food molecules and their collision with the air molecules creates an odor that we can smell. This odor is actually made up of the molecules of the food that have diffused into the air.
The diffusion of the food molecules into the air is a natural process that occurs because of the difference in concentration between the food and the air. This diffusion continues until the concentration of the food molecules in the air reaches equilibrium with the concentration of the food molecules inside the lunch box. At this point, the odor will no longer be noticeable because the concentration of the food molecules in the air will be the same as the concentration of the food molecules inside the lunch box.