The transistor will work as a switch when it operates:

The correct answer is Option (4) → In cut off region and saturation region

A switch has only two states, off and on. In the transfer characteristic of the transistor, the cut off region (low input, output high at \( V_{CC} \), no collector current) is the off state, and the saturation region (high input, output close to zero) is the on state. In the active region the output changes smoothly and almost linearly with the input, which is the region used for amplification, not for switching.

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 as a Device – “… When the transistor is used in the cutoff or saturation state it acts as a switch. On the other hand for using the transistor as an amplifier, it has to operate in the active region.”