Germanium is a semiconductor because:

The correct answer is Option (3) → The band gap of each germanium atomic energy level is small.

Band theory explains conduction. In semiconductors the gap between the filled valence band and the empty conduction band is small. At room temperature some electrons gain enough energy to jump across this gap, so the solid conducts a little, and the conductivity rises with temperature. Pure germanium and silicon behave in this way (intrinsic semiconductors).

Why the other options are incorrect

• Option (1) The band gap of each germanium atomic energy level is large. — Incorrect. A large gap is the feature of an insulator: electrons cannot jump to the conduction band, so the conductivity is very small.

• Option (2) There is overlapping of bands in germanium atoms. — Incorrect. Overlapping (or partly filled) bands are the feature of a metal, where electrons move freely under an applied field.

• Option (4) Germanium conductivity ranges between \(10^{-20}\) to \(10^{-10}\) \(ohm^{-1}m^{-1}\). — Incorrect. This is the range for insulators. Semiconductors have conductivities in the intermediate range, 10⁻⁶ to 10⁴ ohm⁻¹ m⁻¹.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Conduction of Electricity in Semiconductors