Read the following statements with reference to electronic devices.(A…

The correct answer is Option (2) → (B) and (D)

(A) A transistor is used as a rectifier — Incorrect. Rectification is done by a p-n junction diode, which conducts in one direction only. A transistor is used as an amplifier and as a switch.

(B) A zener diode is used as a voltage regulator — Correct. In reverse breakdown the voltage across a Zener diode stays nearly constant over a wide range of current, so it holds the output voltage steady.

(C) A NOT gate is a universal gate — Incorrect. The universal gates are NAND and NOR; every other gate can be built from either of them. A NOT gate alone cannot make an AND or an OR gate.

(D) A transistor is used as an amplifier — Correct. In the active region a small change in base current produces a large change in collector current, so a small signal is amplified.

(E) A photodiode is used as an oscillator — Incorrect. A photodiode is used as a photodetector: its reverse current changes with the light falling on it.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Zener Diode – “… It is designed to operate under reverse bias in the breakdown region and used as a voltage regulator.”

Optoelectronic Junction Devices – “… (i) Photodiodes used for detecting optical signal (photodetectors).”

Transistor: Structure and Action – “… Basically, it was invented to function as an amplifier, a device which produces a enlarged copy of a signal.”

Logic Gates – “… NAND gates are also called Universal Gates since by using these gates you can realise other basic gates like OR, AND and NOT (Exercises 14.16 and 14.17).”