Single displacement reactions or single replacement reactions are reactions in which one substance is replacing another. The replacement of a metallic ion in solution by a metal atom higher in the activity series than the metal in solution is one of such reaction. The positions of the elements on the activity series provides the driving force for the reaction to occur:
One process can be the spread of smell of perfume . Tge particles of perfume mic in the air and reaches every corner of tge room because they are moving
Second can be the smell of food that reaches us in seconds . This case too tells that the aroma of the food particles gets intermixed and come to us .