What measurement indicates the opposition to current flow in a circuit?

Resistance is the correct measurement that indicates the opposition to current flow in a circuit. It quantifies how much a material resists the flow of electric current, measured in ohms. The higher the resistance, the more it opposes the flow of electricity, which is fundamental in determining how much current will flow for a given voltage according to Ohm's Law (V = IR, where V is voltage, I is current, and R is resistance).

In electrical systems, understanding resistance is crucial because it affects power loss within the circuit and plays a vital role in the functioning of various components, such as resistors, which are designed to manage current flow.

The other choices represent different electrical properties: voltage measures electric potential, capacitance measures a component's ability to store charge, and frequency indicates how often an alternating current changes direction. These properties do not directly quantify opposition to current flow like resistance does.