The correct answer is 4 i.e. All examples are correct. Details about the process of Diffusion: The spreading out and mixing of a substance with another substance due to the motion of its particles is called diffusion. It is a property of matter which is based on the motion of its articles. It is the fastest in gases and slowest in solids. The rate of diffusion increase in increasing the temperature of the diffusing substance. The phenomenon of diffusion tells us about the particles of matter that are constantly moving. Light gases diffuse faster than the heavy gases in the environment. There are few examples of diffusion mentioned below for better understanding: The smell of food being cooked reaches us even from a considerable distance by the process of diffusion only. The fragrance of the burning incense sticks spreads all around due to the diffusion of its smoke into the air. The smell of perfume spreads due to the diffusion of perfume vapors into the air.