The ratio of the inertia and viscous forces acting in any flow, ignoring other forces is called as-

Correct option is B

The Reynolds number is used to describe the ratio of inertial forces to viscous forces in a fluid flow. It is a dimensionless number that helps characterize different flow regimes, such as laminar and turbulent flow.
 Froude number: Describes the ratio of inertial forces to gravitational forces, used primarily in open channel flows.
 Weber number: Relates inertial forces to surface tension forces, often used in cases involving droplets or bubbles.
 Euler number: Represents the ratio of pressure forces to inertial forces.
Therefore, the correct answer is (b) Reynolds number.