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The cause of viscosity in gases is:
(A) cohesive force
(B) adhesive force
(C) diffusion.
(D) conductivity.

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Last updated date: 13th Jul 2024
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Answer
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Hint: We know that diffusion is a process of passive transport in which molecules move from an area of higher concentration to one of lower concentration. Diffusion is the movement of a substance from an area of high concentration to an area of low concentration. Diffusion happens in liquids and gases because their particles move randomly from place to place. Diffusion is an important process for living things; it is how substances move in and out of cells.

Complete step by step answer
The viscosity of a gas can be thought of as a measure of its resistance to flow and is
measured in the CGS unit Poise = dyne sec/cm $^{2}$. The viscosity of gases near room temperature are in the CGS unit Poise range, so that is a commonly used unit. Gas viscosity is only weakly dependent on pressure near atmospheric pressure.
In the case of a gas, viscosity results from jumping of molecules from one layer of a gas to another layer. This means that the viscosity of a gas is caused by the transfer of momentum from one gas molecule to another. Thus, increasing the temperature of a gas will increase its momentum and thus the viscosity.
Viscosity in gases arises principally from the molecular diffusion that transports momentum between layers of flow. The kinetic theory of gases allows accurate prediction of the behaviour of gaseous viscosity.

So, the correct answer is option C.

Note: We know that diffusion is very important in the body for the movement of substances eg the movement of oxygen from the air into the blood and carbon dioxide out of the blood into the air in the lungs, or the movement of glucose from the blood to the cells. Diffusion is the movement of molecules from an area of high concentration of the molecules to an area with a lower concentration. The difference in the concentrations of the molecules in the two areas is called the concentration gradient. The kinetic energy of the molecules results in random motion, causing diffusion.