As per common design practice, the three types of hydraulic turbine, in descending order of flow rate, are

The correct answer is Kaplan, Francis, Pelton.

To understand the descending order of flow rate for hydraulic turbines, we can analyze the characteristics and operating conditions of the three major types of turbines:
1. Kaplan Turbine: This is an axial flow reaction turbine. It is designed for low head (water pressure) but high flow rate (discharge) applications. Because the head is low, a large volume of water (high flow rate) must pass through the turbine to generate significant power.
2. Francis Turbine: This is a mixed flow (radial to axial) reaction turbine. It operates under medium head and medium flow rate conditions. It is highly versatile and widely used in intermediate range hydro-power plants.
3. Pelton Turbine: This is an impulse turbine. It is designed for very high head (high elevation drop) but low flow rate applications. Since the pressure head is extremely high, a relatively small flow rate of water is sufficient to generate high power.

Therefore, comparing the flow rate capacities:
Kaplan (High Flow Rate) > Francis (Medium Flow Rate) > Pelton (Low Flow Rate)

Thus, the descending order of flow rate is Kaplan, Francis, Pelton.