Diode is used as a/an

Diode is used as a rectifier. Diode is a device which allows to pass a current only when it is forward biased that’s why if we use one alternating voltage source instead of battery during the negative cycles the diode will be reverse biased and will not allow the current to flow. Hence, it can be used as a rectifier.

Final Answer: Hence, the correct option is B i.e., rectifier.