Answer:
a. diffusion
Explanation:
It is diffusion which allows us to smell perfume at a distance from the source. Diffusion is a natural phenomenon which occurs when there is a concentration gradient in the molecules of a gaseous substance. The molecules tend to move passively from a place where gradient is higher to a place where gradient is lower by the process of diffusion. This movement continues unless the concentration of molecules become equal at both the places. At this time, an equilibrium is said to be attained and there is no net movement.
In this example, when a bottle of perfume which is source is opened at a distantly located place at that time the concentration gradient of perfume molecules is greater at that place while at a distantly located place where we are standing there are no perfume molecules i.e. concentration of perfume molecules is low . Since there is a gradient so molecules will start to move from source towards us because movement is supposed to be from higher to lower gradient. As a result of which the perfume molecules will reach us by the process of diffusion and we are able to smell the perfume.
