A streamline is defined as the line A. parallel to central axis flow B. parallel to outer surface of pipe C. of equal yelocity in a flow D. along which the pressure drop is uniform

The correct answer is: C. of equal velocity in a flow.

A streamline is a line that is tangent to the velocity vector at each point along its length. This means that the velocity of the fluid is the same at all points along a streamline.

Option A is incorrect because a streamline

is not necessarily parallel to the central axis of flow. For example, in a turbulent flow, the streamlines are often curved and do not follow a straight line.

Option B is incorrect because a streamline is not necessarily parallel to the outer surface of a pipe. For example, in a laminar flow, the streamlines are parallel to the pipe wall, but in a turbulent flow, the streamlines are often curved and do not follow a straight line.

Option D is incorrect because the pressure drop is

not necessarily uniform along a streamline. For example, in a converging-diverging nozzle, the pressure drop is higher in the converging section than in the diverging section.

In conclusion, the correct answer is C. of equal velocity in a flow.