Which of the following symbols represents a resistor in a circuit diagram?

The symbol representing a resistor in a circuit diagram is denoted by Ω, which is the Greek letter "omega" and signifies the unit of electrical resistance known as ohms. This unit measures a resistor's ability to impede the flow of electric current.

In circuit diagrams, components are represented by symbols that provide a visual understanding of how they interact within a circuit. The use of Ω for a resistor effectively communicates to anyone looking at the diagram that the component in question is meant to resist the flow of electricity.

The alternative options represent other electrical concepts: R typically signifies resistance as a variable but isn't the specific symbol for a resistor in the graphical sense. V denotes voltage, illustrating the electric potential difference, while I represents current or the flow of electric charge through a circuit. The distinction between these terms is essential for understanding circuit functionality and design, but they do not serve as the symbol for a resistor itself.