What unit measures the resistance to the flow of electrical current?

The correct answer is based on the understanding of basic electrical concepts. Resistance to the flow of electrical current is measured in Ohms. An Ohm quantifies how much a material opposes the flow of electric current. The relationship is defined by Ohm's Law, which states that voltage (measured in volts) equals current (measured in amperes) multiplied by resistance (measured in ohms).

In this context, the other options refer to different aspects of electrical measurements: Volts measure electrical potential or pressure, Amperes measure the flow rate of electric charge, and Watts measure power, which is the product of voltage and current. Therefore, when specifically discussing the aspect of resistance in an electrical circuit, Ohms is the appropriate and correct unit.