Final answer:
The rectifier that requires four diodes is the Full Wave Bridge Rectifier which converts AC to DC more efficiently by using both halves of the AC waveform.
Step-by-step explanation:
The rectifier that requires the use of four diodes is B. Full Wave Bridge Rectifier. In a full wave bridge rectifier, the four diodes are connected in a bridge configuration to efficiently convert an alternating current (AC) input into a direct current (DC) output. This rectifier allows for both halves of the AC waveform to be used, unlike a half wave rectifier which only uses one half of the waveform.
By utilizing all parts of the input signal, the full wave bridge rectifier is more efficient and provides a smoother DC output compared to the half wave rectifier.