GATE Chemical Engineering 2020 Question 43: Wall Shear Stress Ratio in Laminar, Fully Developed Pipe Flow

Consider steady, laminar, fully developed flow of an incompressible Newtonian fluid through two horizontal straight pipes, I and II, of circular cross section. The volumetric flow rates in both the pipes are the same. The diameter of pipe II is twice the diameter of pipe I, i.e., d_II=2d_I. The ratio of the shear stress at the wall of pipe I to the shear stress at the wall of pipe II is