Which of the following statements are correct for a transistor action…

The correct answer is Option (4) → (A) and (C) only

Note: The given answer is as per the official NTA Answer Key. However, none of the given options appears to be correct; the correct set is (A), (C) and (D), as explained below.

Transistor action (the active region) needs the emitter-base junction forward biased and the collector-base junction reverse biased. The currents are related by

    \( \displaystyle I_E = I_B + I_C \)

(A) The input resistance depends upon the current \( I_e \) in the transistor — Correct. The input resistance \( r_i = \Delta V_{BE}/\Delta I_B \) comes from the curved input characteristic, so its value changes with the current.

(B) Collector currents is equal to the sum of base current and emitter current — Incorrect. It is the emitter current that is the sum, \( I_E = I_B + I_C \); the collector current is \( I_C = I_E - I_B \), smaller than \( I_E \).

(C) The emitter junction is forward biased — Correct. Forward bias lets the emitter inject majority carriers into the base.

(D) The collector junction is reverse biased — Correct. Reverse bias on the collector junction sweeps the carriers arriving from the base into the collector.

(E) Both the emitter junction as well as the collector junction are forward biased — Incorrect. With both junctions forward biased the transistor is in saturation, not in the active region.

The correct set (A), (C) and (D) is not among the options, and it seems that NTA has assumed (D) to be incorrect.

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):
Exercises – …