ANS:B - 2/3

The maximum efficiency of transmission of power (ηmax​) in a pipe occurs when the loss of head due to friction (f1) is equal to one-third of the total head available at the inlet of the pipe, not 1/2 as previously mentioned. Here's the explanation: The efficiency of power transmission (η) in a pipe system is given by: η=H−f1/H​​ Where:

• H is the total head available at the inlet of the pipe.
• f1​ is the loss of head due to friction in the pipe.

For maximum efficiency (ηmax​), we want to maximize η. This occurs when f1​ is minimized relative to H. In this case, the maximum efficiency of transmission of power (ηmax​) occurs when f1​ is one-third of H, because it's the point where the friction losses are balanced with the available head, maximizing the efficiency. Therefore, the correct answer is: 2/3