Zener diodes are used as (A) amplifiers (B) voltage regulators (C) oscillators (D) half-wave rectifiers

Zener diodes are a special type of semiconductor diode which allows current to flow in the forward direction like a regular diode, but also allows it to flow in the reverse direction when the voltage across it exceeds a certain breakdown voltage (called Zener voltage). This property makes them useful for voltage regulation and protection applications.

Now let us consider each option and see if it is the main application of Zener diodes: (A) Amplifiers: Zener diodes are not generally used as amplifiers because they are designed to maintain a specific voltage, not amplify a signal. (B) Voltage regulators: Zener diodes are used as voltage regulators since they can maintain a stable output voltage even when the input voltage varies. When the input voltage exceeds the Zener voltage, the diode will conduct in reverse, keeping the output voltage at the Zener voltage. (C) Oscillators: Oscillators are electronic circuits that generate an output signal without any input. Zener diodes are not primarily used in oscillator circuits. (D) Half-wave rectifiers: Rectifiers are used to convert alternating current (AC) to direct current (DC). Zener diodes may sometimes be involved in rectifier circuits, but it's not their primary application.

After evaluating each option, we can conclude that the primary application of Zener diodes is as voltage regulators. Thus, the correct answer is: (B) Voltage regulators