Given below are two statements :
Statement (I) :Viscosity of gases is greater than that of liquids.
Statement (II) : Surface tension of a liquid decreases due to the presence of insoluble impurities.
In the light of the above statements, choose the most appropriate answer from the options given below :

Solution

Physics sir · 3 steps

Judge each statement alone: compare air with water, then ask where an insoluble impurity sits.

1. Statement I. Water has viscosity about 1.0 × 10⁻³ Pa s, but air has only about 1.8 × 10⁻⁵ Pa s, so water is roughly 50 times more viscous. Gas molecules are far apart, so there is little resistance between moving layers, which makes Statement I incorrect.
2. Statement II. An insoluble impurity, such as dust or a film of oil, cannot mix into the liquid, so it collects on the surface. There it weakens the cohesive pull between the surface molecules, and the surface tension falls. So Statement II is correct.
3. So. Statement I is incorrect and Statement II is correct, which is option (b).

The idea to keep. Liquids are more viscous than gases, because liquid molecules are close together. Impurities that stay on the surface of a liquid lower its surface tension.

Answer from the NTA final answer key. Solution by PrepWiser.