By what mechanism does scent spread all over the room if the lid is opened ?

The spreading of scent throughout a room when a bottle is opened is primarily due to the process of diffusion. Diffusion is defined as the movement of particles from an area of higher concentration to an area of lower concentration due to random thermal molecular motion. When the lid is opened, the concentrated scent molecules in the bottle escape and collide with air particles, which are in constant motion [1]. These collisions help the fragrance particles spread evenly throughout the available space [2]. Unlike osmosis, which requires a semi-permeable membrane and typically involves liquid solvents, diffusion occurs in solids, liquids, and gases. While pressure differences can influence the initial release, the long-range dispersal across a room is a classic example of molecular diffusion in a gaseous medium [2].

Sources

1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 7: Particulate Nature of Matter > Activity 7.9: Let us find out > p. 111
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 26: Tropical Cyclones > Vapour Pressure of Water And Rate of Evaporation > p. 358