Which of the following are semiconductors?
(A) CuO
(B) Si
(C) Glass
(D) Ge
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (D) only
Solids are classed by their electrical conductivity, which is explained by the energy gap between the filled valence band and the empty conduction band:
Conductors (metals): the bands overlap or the valence band is partly filled, so electrons move freely.
Insulators: the gap is very large, so electrons cannot jump into the conduction band.
Semiconductors: the gap is small; some electrons jump across, and the conductivity (between about 10−6 and 104 S m−1) increases with temperature.
(A) CuO — Correct. Copper(II) oxide is a p-type oxide semiconductor.
(B) Si — Correct. Silicon is the most common intrinsic semiconductor.
(C) Glass — Incorrect. Glass has a very large energy gap and is an insulator.
(D) Ge — Correct. Germanium, in the same group as silicon, is an intrinsic semiconductor.
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.