Question

Which of the following correctly states how the viscosities of a liquid and a gas will change with temperature?

• A. Viscosity increases with increase in temperature of a liquid and decreases with the increase in temperature of a gas
• B. Viscosity increases with increase in temperature of a liquid and increases with the increase in temperature of a gas
• C. Viscosity decreases with increase in temperature of a liquid and decreases with the increase in temperature of a gas
• D. Viscosity decreases with increase in temperature of a liquid and increases with the increase in temperature of a gas

Answer 1

The correct option is D Viscosity decreases with increase in temperature of a liquid and increases with the increase in temperature of a gas

In case of liquids, if we increase the temperature then the distance between the molecules is going to increase and then the cohesive force will decrease. Thus the viscosity will decrease.
$T\propto \frac{1}{Viscosity}$
In the case of gases the dominant force is molecule momentum transfer, not cohesive force because gas is free to move so, if we increase the temperature then the collisions between gas molecule will increase the viscosity.
$T\propto Viscosity$
So option D is correct