Question

________ is a process of gradual mixing of two substances kept in contact with each other.

Answer 1

Kinetic theory of gases: It states that the molecules are always in a constant linear motion and takes up negligible amount of volume in the container. It also states that no energy is gained or lost during the collisions of molecules.

Complete answer:
According to the kinetic theory of gases, all the molecules or particles are in linear motion which causes collision of molecules with each other as well as with walls of containers. So, two process takes place during the motion of these particles which are as follows:
Diffusion: It refers to the process of moving of particles from the area of high concentration towards low concentration. This movement depends on the size of the particles as well as the temperature and viscosity of the medium. It results in the gradual mixing of two particles or substances kept in contact with each other and at last forms a homogeneous mixture.
Effusion: It is the continuous random motion of the particles which make sure that some particles at last will pass through a small hole. The diameter of the hole through which the particles are passing must be smaller than the mean free path of the molecule.
Hence, Diffusion is the process of gradual mixing of the two substances or particles when kept in contact with each other.

Note:
Osmosis: The movement of solvent molecules from the region of high solvent potential towards the low solvent potential through a semipermeable membrane is termed as osmosis. It is different from the diffusion because in diffusion both solvent and solute particles are allowed to move whereas in osmosis, only solvent particles move freely.