The function of a diode can be:

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

A p-n junction diode conducts easily when forward biased and hardly at all when reverse biased, so current passes through it in one direction only. An alternating voltage applied through a diode therefore gives a current that flows in one direction only: this is rectification, the conversion of ac into (pulsating) dc.

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. This property is used to rectify alternating voltages and the circuit used for this purpose is called a rectifier.”