ANS:A - mechanical

In the case of a centrifugal pump, the ratio ℎ1ℎ2​ is termed as the volumetric efficiency. The term "volumetric efficiency" refers to the ratio of the actual measured head (h1) to the head imparted to the fluid by the impeller (h2). It represents the effectiveness of the pump in transferring fluid energy from the impeller to the fluid. Volumetric efficiency accounts for losses such as friction, leakage, and inefficiencies within the pump that may reduce the actual head delivered compared to the theoretical head imparted by the impeller. It provides insight into the pump's ability to deliver the desired flow rate and pressure under real-world operating conditions. Other efficiencies, such as mechanical efficiency and overall efficiency, evaluate different aspects of the pump's performance, such as the efficiency of converting mechanical power into hydraulic power (mechanical efficiency) and the overall efficiency of the pump system, including both hydraulic and mechanical losses (overall efficiency). However, the ratio ℎ1ℎ2h2h1​ specifically represents the volumetric efficiency in the context of centrifugal pumps.