The lighting of an incense stick in one corner of a room and the subsequent spreading of the odor to different parts of the room is an example of diffusion. Lighting a cigarette causes the smoke to spread to all parts of the room due to diffusion.
Diffusion involves the movement of particles from a region of high concentration to a region of low concentration. Diffusion can take place in a liquid medium as well, but it is faster in a gaseous medium. For example, when a drop of ink is added to water in a beaker, the ink is seen spreading gradually to all parts of the water in the beaker. When perfume or deodorant is sprayed in one corner of a room, the fragrance spreads rapidly due to diffusion.