At what speed does the radio wave travel?

Radio, infrared, ultraviolet, X-rays, gamma Ray's, and light that you can see, are all electromagnetic waves, and all travel at the "speed of light".

Exactly: 299,792,458 meters per second, in vacuum

Easier to remember: 300,000 kilometers per second, in vacuum

Slower in any material stuff. Depends on the substances.

Reynolds number = the ratio of inertial to viscous forces

Explanation:

Reynolds number is defined as :

Where

is flow speed

D is diameter of the tube

is  kinematic viscosity of the fluid

Reynolds number is defined as the ratio of inertial forces to viscous forces within a fluid which is subjected to relative internal movement due to different fluid velocities.So, the correct option is (b) "ratio of inertial to viscous forces".