What does resistance (measured in ohms) in a circuit limit?

Resistance, measured in ohms, directly refers to how much a material or device within an electrical circuit opposes the flow of electric current, which is primarily the movement of electrons. When resistance is present in a circuit, it impedes the flow of these electrons, thereby limiting the overall current that can pass through at a given voltage, as described by Ohm's Law (V = I * R). As such, higher resistance means less current (or fewer electrons) flowing through the circuit for a given voltage.

This fundamental aspect of resistance also affects energy transfer in the circuit. When some energy is converted into heat due to the resistance, less energy is available for use in powering devices connected to the circuit. Therefore, resistance plays a crucial role in determining both how many electrons can flow and how efficiently energy is transferred within that circuit.

The other potential answers touch on different aspects of electrical circuits but do not accurately describe the specific role of resistance. For instance, resistance does not limit the flow of protons, voltage, or the capacitance of the circuit, which are distinct concepts separate from the opposition to current flow.