Final answer:
An impeller with backward curved vanes has a falling head - discharge characteristic, where the pressure head decreases as the discharge increases.correct option in the final answer is A.
Step-by-step explanation:
With reference to an impeller with backward curved vanes, the correct statement is that it has a falling head - discharge characteristic.
This means that as the flow rate (discharge) increases, the pressure head provided by the impeller decreases. Backward curved vanes are designed to deliver stable performance and high efficiency with a decrease in the risk of overloading the motor at high flow rates.
They are also known to have good non-overloading characteristics which mean they are designed to prevent the motor from drawing more power than it can handle, even when operating at flow rates beyond the design point.
Therefore, the mentioned It has a falling head - discharge characteristic.