Correct Answer - Option 2 : Dependent on relative roughness of pipe only

Friction factor (f) for turbulent flow rough pipe is a function of relative roughness only.

\(\frac{1}{{\sqrt f }} = 2\log \left( {\frac{R}{K}} \right) + 1.74\)

for laminar flow Friction factor ⇒ \(f = \frac{{64}}{{Re}}\)

For laminar flow friction factor depends only upon the Reynolds number of the flow and is independent of the contact surface.