Which of these components can be used as an electronic switch?

A transistor is a versatile semiconductor component used primarily to amplify or switch electrical signals and power. By applying a small voltage or current to one of its terminals, it can control a much larger current flowing through its other terminals, effectively acting as an electronic switch turning a circuit on or off. Other options are variable components but not solid-state switches. A potentiometer is a variable resistor used for things like volume controls, while varistors and thermistors change their resistance based on voltage spikes or temperature changes, respectively.