A flow in which the quantity of liquid flowing per second is constant, is called __________ flow.

A flow in which the quantity of liquid flowing per second remains constant is referred to as steady flow.

Steady Flow:
In steady flow, the flow parameters such as velocity, pressure, and density do not change with time at any given point. This means that the amount of liquid flowing per second (the flow rate) remains constant over time.

Streamline Flow:
Streamline flow, also known as laminar flow, describes the smooth, orderly movement of fluid in which layers of fluid flow parallel to each other. While streamline flow can be steady, it is not specifically defined by the constancy of flow rate.

Turbulent Flow:
Turbulent flow is characterized by chaotic and irregular fluid motion, where the flow rate can fluctuate. It is not defined by a constant flow rate.

Unsteady Flow:
Unsteady flow occurs when the flow parameters change with time at any given point. This means that the flow rate is not constant, and the quantity of liquid flowing per second can vary.

Therefore, the correct answer is Option A: Steady.