Which electrical unit is used to measure a material's opposition to the flow of electricity?

The correct choice is based on the fact that the unit used to measure a material's opposition to the flow of electricity is the ohm. The ohm (symbol: Ω) is a fundamental unit in electrical engineering and physics. It quantifies how much a specific material resists the flow of electric current. When a voltage (measured in volts) is applied across a conductor, the ohm captures the relationship between the voltage and the current flowing through the material.

Understanding this measurement is crucial for various applications, including designing electrical circuits and ensuring safety and efficiency in electrical systems. Resistance, which is the property of a material that quantifies its opposition to electrical current, is measured in ohms. Impedance is a broader concept that applies to alternating current (AC) circuits, combining resistance with the effects of capacitance and inductance, but the fundamental unit remains the ohm.

The other options represent different electrical concepts: amperes measure electric current, volts measure electric potential, and resistance or impedance describes properties rather than serving as a specific unit. Thus, the selection of the ohm as the correct answer accurately reflects the appropriate unit for measuring opposition to the flow of electricity.