The correct answer is (d) the frictional resistance is independent of the nature of the surface area of contact when the liquid flows at a velocity less than the critical velocity
Explanation: Frictional resistance is dependent on the nature of the surface area of contact. But, when the liquid flows at a velocity less than the critical velocity, a thin stationary film of the liquid is formed on the supporting surface. Hence, the frictional resistance becomes independent of the nature of the surface of contact.