Viscous forces are not present in

Explanation

Viscous forces, which result from the internal friction between layers of fluid in motion, are present in many types of fluid flows. In the context of this question, rotational, irrotational, and laminar flows can all exhibit viscous forces. Rotational flow involves the rotation of fluid elements, but this motion does not imply the absence of viscosity. Irrotational flow may not have fluid particle rotation, yet viscosity can still affect the flow. Laminar flow is characterized by smooth and orderly layers, typically at low velocities, where viscous forces are prominent in maintaining the layer structure. Therefore, the correct answer is 'None of these,' as viscous forces can be present in all the given types of flow.