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

The correct option is Kaplan, Francis, Pelton.

To understand why this is the correct order, we can analyze the design characteristics and operating conditions of these three primary types of hydraulic turbines:

1. Kaplan Turbine:
This is an axial flow reaction turbine. It is designed to handle very large quantities of water (high flow rates) but operates under low hydraulic heads (typically less than 30 meters). To produce significant power from a low head, a very large volume of water must pass through the turbine, making it the turbine with the highest flow rate capacity.

2. Francis Turbine:
This is a mixed flow (radial and axial) reaction turbine. It operates under medium heads (typically ranging from 30 meters to 300 meters) and medium flow rates. It sits in the intermediate range between the high-flow Kaplan turbine and the low-flow Pelton turbine.

3. Pelton Turbine:
This is an impulse turbine. It is designed for very high hydraulic heads (often exceeding 300 meters) but requires relatively small quantities of water (low flow rates). High pressure is converted into high-velocity kinetic energy jets that strike the buckets, meaning a much smaller volume of water is needed to generate power compared to reaction turbines.

Therefore, when arranged in descending order of flow rate capacity, the sequence is:
Kaplan > Francis > Pelton