Concept: Viscosity: • It is a measure of resistance to flow which arises due to internal friction between layers of fluid as they slip past one another as the liquid flows. • The coefficient of viscosity is defined as the force per unit area required to maintain the unit difference of velocity between two parallel layers unit length apart. Density: • The mass density or density of a material is defined as its mass per unit volume. • The symbol most often used for density is 'ρ' (rho). • Mathematical Expression is \(\rm Density= {Mass \over Volume}\) • The density depends on external factors such as temperature and pressure. • Aso, density depends on the nature of the substance. Diffusion • It is the intermixing of two or more gases irrespective of density relationship and without the help of an external agency. • The rate of diffusion is seen to be inversely proportional to the square roots of their densities under similar conditions of temperature and pressure. This is known as Graham's law of diffusion. • Mathematically, we can say: \(r = \sqrt{1 \over d}\), where r = rate and d = density Explanation: • Viscosity is the natural resistance to the flow of gas molecules. • Viscosity in gases arises due to the jumping of molecules from one layer to the other layer. • Viscosity in gases is the transfer of momentum from one molecule to the other. • Gases when provided in an open space, escape from their vessel and mixes with the other gases present in the surroundings. • This occurs due to diffusion, it is seen that gases with low molecular masses move and intermix more quickly than those of heavier ones. • So, it can be said that the lighter gases diffuse more quickly than the heavier ones. • Density is the intensive property of a gas. • So, when in a closed room perfume bottle is opened up, gas molecules are released into the air. • These gas molecules transfer very fast to the areas of low concentration of them and soon are spread all over the room. • This occurs due to the diffusion of gases, and the whole room develops smell. Hence, the property of gas that is responsible for this is Diffusion.