ANS:D - 66.67%

The efficiency of power transmission through a pipe cannot be 66.67% in most practical scenarios. The reason is that efficiency values for power transmission, especially through pipes, tend to be less than 100% due to inherent losses in the system such as frictional losses, turbulence, and other factors. Efficiency is a measure of how well a system converts input power into useful output power. In the context of fluid dynamics and pipe systems, the efficiency of power transmission refers to how much of the input power (usually in the form of fluid flow) is effectively utilized for the desired output (such as mechanical work or energy delivery). In practical situations, the efficiency of power transmission through a pipe system is often less than 100% due to various factors:

1. Frictional losses: As fluid flows through a pipe, it encounters resistance from the walls of the pipe and internal friction within the fluid itself, leading to energy losses in the form of heat.
2. Turbulence: Irregularities in the flow, sudden changes in direction, or obstructions in the pipe can create turbulence, causing additional energy losses.
3. Bends, fittings, and valves: Changes in direction, pipe fittings, and valves introduce additional resistance and energy losses.

Due to these factors, the efficiency of power transmission through a pipe system is typically less than 100%. Achieving an efficiency of 66.67% in a pipe system would imply that two-thirds of the input power is effectively utilized for the desired output, which is usually not achievable in most practical scenarios. Therefore, while theoretical calculations and design considerations can estimate efficiencies, achieving such high values in real-world pipe systems would require exceptionally well-designed and maintained systems with minimal losses, which is rare.