What is the function of a diode in electrical circuits?

A diode is designed to allow current to flow in only one direction while blocking it in the opposite direction. This property makes diodes essential components in various applications, such as rectification in power supplies, where alternating current (AC) must be converted into direct current (DC). When the diode is forward-biased, it conducts electricity, enabling current flow; when reverse-biased, it effectively acts as an open circuit, preventing current flow.

Amplifying signals, storing energy, or switching electrical signals are functions typically associated with other components. For instance, transistors are used for amplification, capacitors for energy storage, and relays or transistors for switching functions. Therefore, the defining characteristic of a diode is its ability to limit current to one direction, confirming the correct answer.