Rotameter is a device used to measure A. absolute pressure B. velocity of fluid C. flow D. rotation

The correct answer is C. flow.

A rotameter is a variable-area flowmeter used to measure the flow rate of a liquid or gas. It consists of a tapered tube with a float inside. The float is held up by the upward force of the flowing fluid, and its position in the tube indicates the flow rate.

The other options are incorrect because:

• A. absolute pressure is the pressure of a fluid relative to a perfect vacuum.
• B. velocity is the rate of change of position of an object.
• D. rotation is the circular movement of an object around an axis.