ANS:D - all (a), (b) and (c).

The capacity of a centrifugal pump can be increased by:

• Increasing the impeller diameter or speed.
• Increasing the number of pumps and joining them in parallel.

Explanation:

1. Impeller Diameter or Speed:
   • Increasing the diameter of the impeller or increasing the rotational speed of the pump will increase the kinetic energy imparted to the fluid. This leads to an increase in flow rate (capacity) through the pump.
2. Number of Pumps in Parallel:
   • When multiple pumps are operated in parallel (side by side), the combined flow rate is the sum of the flow rates of each individual pump. This effectively increases the total capacity of the pumping system.
3. Number of Pumps in Series:
   • When pumps are operated in series (one after another), the head generated by each pump adds up, but the flow rate remains the same as that of a single pump. Operating pumps in series is primarily used to increase the total head rather than the flow rate.
4. All (a), (b), and (c):
   • While increasing impeller diameter or speed directly increases flow rate, and operating pumps in parallel also increases flow rate, operating pumps in series primarily increases head rather than flow rate. Therefore, option (c) is not entirely correct.

Conclusion:

• Increasing the impeller diameter or speed directly increases the pump's capacity.
• Increasing the number of pumps and joining them in parallel increases the total flow rate capacity of the pumping system.