What device is known to allow current to flow in one direction based on polarity?

A diode is a semiconductor device that allows current to flow in only one direction. It is designed to control the direction of current flow by utilizing its structure, which typically consists of a p-n junction. When a positive voltage is applied to the anode and a negative voltage to the cathode, the diode enters a conductive state, allowing current to pass through. If the polarity is reversed, the diode becomes non-conductive, effectively blocking current flow. This property makes diodes essential in various applications, such as rectifiers in power supply circuits, signal modulation, and protection circuits, ensuring that devices are safeguarded against inadvertent reverse polarity.

In contrast, resistors, inductors, and capacitors do not have the same directionality in current flow. Resistors oppose current flow regardless of its direction, inductors store energy in a magnetic field and can oppose changes in current flow, while capacitors store electrical energy and release it based on voltage changes. Hence, the distinguishing feature of a diode is its ability to manage current based on polarity, making it the correct choice for this question.