A p-n junction diode can be used:

The correct answer is Option (2) → to convert ac voltage into dc voltage

A p-n junction diode conducts when it is forward biased and blocks current when it is reverse biased. With an ac input it passes current in one half-cycle only, so the output current flows in one direction. This use of the diode is called rectification.

NCERT (2026-27):
Application of Junction Diode as a Rectifier – “From the V-I characteristic of a junction diode we see that it allows current to pass only when it is forward biased. So if an alternating voltage is applied across a diode the current flows only in that part of the cycle when the diode is forward biased.”