In a transistor:(A) one of the outer layers is heavily doped and is c…

The correct answer is Option (2) → (B), (C) and (E) only

A bipolar junction transistor has three layers. The emitter must supply a large number of majority carriers, so it is heavily doped; the base is very thin and lightly doped so that most carriers pass through it; the collector is moderately doped and larger in size, to collect the carriers.

(A) one of the outer layers is heavily doped and is called collector — Incorrect. The heavily doped outer layer is the emitter; the collector is moderately doped.

(B) one of the outer layers is heavily doped and is called emitter — Correct. Heavy doping lets the emitter supply many carriers.

(C) the middle layer is very lightly doped and is called base — Correct. A thin, lightly doped base lets most carriers cross to the collector.

(D) one of the outer layer is moderately doped and is called emitter — Incorrect. The emitter is heavily, not moderately, doped.

(E) one of the outer layer is moderately doped and is called collector — Correct. The collector is the moderately doped outer layer.

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 – “… A brief description of the three segments of a transistor is given below: Emitter: This is the segment on one side of the transistor shown in Fig. 14.27(a). It is of moderate size and heavily doped. Base: This is the central segment. It is very thin and lightly doped. Collector: This segment collects a major portion of the majority carriers supplied by the emitter. The collector side is moderately doped and larger in size as compared to the emitter.”