The correct answer is B. unsteady.
Steady flow is a type of fluid flow in which the fluid properties (velocity, pressure, density, etc.) at a given point in space do not change with time. Unsteady flow is a type of fluid flow in which the fluid properties at a given point in space do change with time.
When a valve is opened in a pipe line, the flow is unsteady because the fluid properties at a given point in space change with time. The velocity of the fluid increases as the valve is opened, and the pressure of the fluid decreases.
The other options are incorrect. Option A, steady flow, is incorrect because the flow is unsteady. Option C, uniform flow, is incorrect because the flow is not uniform. The velocity of the fluid is not the same at all points in the pipe. Option D, laminar flow, is incorrect because the flow is not laminar. Laminar flow is a type of fluid flow in which the fluid particles move in smooth, parallel layers. The flow of fluid through a pipe is not laminar when the valve is opened.