What is typically associated with impulse-reaction turbines?

Impulse-reaction turbines are characterized by the conversion of pressure energy into mechanical energy through both the impulse and reaction principles. In these turbines, steam or another working fluid undergoes a significant drop in both pressure and temperature as it passes through the turbine blades. The first stage, which operates on the impulse principle, transforms the pressure of the steam into kinetic energy, which then impacts the turbine blades, causing rotation. As the steam continues through subsequent stages of the turbine, it expands and undergoes a further drop in pressure, leading to a notable decrease in temperature as well.

This large drop in both pressure and temperature is essential for maintaining the efficiency of impulse-reaction turbines, as it facilitates the production of work from the turbine. Other options do not align with the operational characteristics of these turbines. For instance, a constant pressure drop would suggest a steady-state process that is not typical for impulse-reaction turbines, while a gradual temperature increase would contradict the principles of thermodynamics governing their operation. A small pressure drop does not capture the substantial energy transformation that occurs throughout the impulse-reaction process.