Consider following statements:
A. Surface tension arises due to extra energy of the molecules at the interior as compared to the molecules at the surface, of a liquid.
B. As the temperature of liquid rises, the coefficient of viscosity increases.
C. As the temperature of gas increases, the coefficient of viscosity increases
D. The onset of turbulence is determined by Reynold's number.
E. In a steady flow two stream lines never intersect.
Choose the correct answer from the options given below:

Solution

Physics sir · 3 steps

Check each statement on its own: liquids and gases behave opposite ways when heated.

1. Statement A. Surface molecules have fewer neighbours pulling on them, so they carry extra energy compared with interior molecules. A says the reverse, so A is false.
2. Statements B and C. In a liquid, heating weakens the cohesive forces between molecules, so viscosity decreases. In a gas, viscosity comes from molecules carrying momentum between layers, and faster molecules carry more, so it increases. B is false and C is true.

   Statement	Physics behind it	Verdict
   A	Extra energy belongs to surface molecules, not interior ones	False
   B	Liquid viscosity falls as temperature rises	False
   C	Gas viscosity rises as temperature rises	True
   D	Turbulence sets in when Reynolds number crosses a critical value	True
   E	Crossing streamlines would give two velocities at one point	True

3. So. The true statements are C, D and E, which is option (b).

The idea to keep. Heat a liquid and its viscosity drops because cohesion weakens. Heat a gas and its viscosity rises because momentum transfer grows. Surface molecules, not interior ones, carry the extra energy.

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