Ncert Exercises & Solutions

With an increase in temperature, the viscosity of:

(a)	gases decrease.	(b)	liquids increase.
(c)	gases increase.	(d)	liquids decrease.

Which of the following options is/are correct?
1. (b), (c)
2. (a), (d)
3. (c), (d)
4. (a), (b)

(3) Hint: The viscosity of a liquid depends on the intermolecular forces and the viscosity of the gases depends on the movement of the molecules.

Step 1: Find the variation of viscosity of the liquids with temperature.
For liquids, the coefficient of viscosity,

η_{l i q u i d} \propto \frac{1}{\sqrt{T}}

i.e. with an increase in temperature,

η_{l i q u i d}

decreases.

Step 2: Find the variation of viscosity of the gases with temperature.
For gases, the coefficient of viscosity,

η_{g a s e s} \propto \sqrt{T}

i.e. with an increase in temperature,

η_{g a s e s}

increases.