ANS:D - all the above.

The correct statement from the options provided is: Vertical distance between the total energy line and hydraulic grade line is equal to the velocity head. In fluid mechanics, the hydraulic grade line (HGL) represents the total energy of the fluid per unit weight, including pressure head, elevation head, and velocity head. The total energy line (TEL) represents the sum of pressure head, elevation head, and velocity head at any point along the pipe. The vertical distance between the total energy line and the hydraulic grade line is indeed equal to the velocity head. This distance represents the energy associated with the velocity of the fluid flow in the pipe. The other statements provided are not universally true:

• The first statement is incorrect because the total energy gradient represents the change in total head along the length of the pipe, not at any specific section.
• The third statement is incorrect because the vertical distance between the total energy line and total energy gradient does not represent loss of head; rather, it represents the change in total head along the length of the pipe.