Which of the following is an electrical safety device?

A circuit breaker is an electrical safety device designed to protect electrical circuits from overload and short circuits. When the current flowing through a circuit exceeds a predetermined level, the circuit breaker automatically interrupts the flow of electricity. This prevents excessive current from causing overheating, which could lead to fires or damage to electrical components. By automatically shutting off the power, circuit breakers help ensure the safety of the electrical system and the equipment connected to it.

Other options, while crucial components in electrical systems, do not serve the primary function of safety protection. A transformer is used to change voltage levels, a capacitor stores electrical energy, and a resistor limits the flow of current in a circuit. None of these components provide the same protective capabilities as a circuit breaker, which makes it the correct choice for this question.