For a transistor to be used as an amplifier its input and output regions should be biased respectively in:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Forward and reverse biasing
A transistor works as an amplifier in its active state, with the emitter-base (input) junction forward biased and the base-collector (output) junction reverse biased.
The forward biased input junction has a low resistance and lets the emitter send its majority carriers into the thin base. The reverse biased output junction has a high resistance and sweeps almost all of these carriers into the collector, so the collector current is almost equal to the emitter current while it flows through a large load resistance. A small input voltage therefore produces a large output voltage.
Why the other options are incorrect
Option (2) Forward and forward biasing — Incorrect. Both junctions conduct and the transistor is in saturation, where it acts as a closed switch.
Option (3) Reverse and forward biasing — Incorrect. The emitter then no longer injects carriers into the base, so there is no useful amplification.
Option (4) Reverse and reverse biasing — Incorrect. Neither junction conducts and the transistor is in cut off, where it acts as an open switch.
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):
Transistor: Structure and Action – “… The transistor works as an amplifier, with its emitter-base junction forward biased and the base-collector junction reverse biased.”