What type of flow is characterized by a constant amount of fluid particles passing through a pipe section at any given moment?

Steady flow is defined as a condition in which the velocity of the fluid at any given point does not change with time. This means that, at any specific location within the pipe, the flow characteristics—such as speed, pressure, and density—remain constant over time. When referring to the constant amount of fluid particles passing through a section of the pipe, it indicates that the flow rate is stable, and the same volume of fluid crosses that section in a given time period.

In contrast, unsteady flow signifies that these parameters vary with time, leading to changes in velocity and flow rate at various points within the system. Turbulent flow describes a chaotic state where fluid particles move in random patterns, which does not align with the notion of a consistent flow rate. Laminar flow, characterized by smooth, orderly layers of fluid, can also be steady, but it is primarily defined by the nature of the flow rather than the temporal stability of the flow parameters.

Therefore, the stability and constancy of the fluid's movement in steady flow make it the correct choice for the scenario described in the question.