Important electronic devices are not made from intrinsic semiconductors. The main reason is that
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → their conductivity at room temperature is very low
Option (1) they have no free charge carriers at room temperature — Incorrect. At room temperature, thermal energy breaks a few covalent bonds. So a small number of free electrons and holes are present.
Option (2) their conductivity does not depend on temperature — Incorrect. The conductivity of an intrinsic semiconductor depends on temperature. It rises as more bonds break.
Option (3) their conductivity at room temperature is very low — Correct. Only a few carriers are present at room temperature, so the conductivity is very low. Doping is used to raise it.
Option (4) the numbers of free electrons and holes in them are not equal — Incorrect. Each broken bond gives one free electron and one hole, so \( n_e=n_h \) in an intrinsic semiconductor.
NCERT (2026-27):
Extrinsic Semiconductor – “The conductivity of an intrinsic semiconductor depends on its temperature, but at room temperature its conductivity is very low. As such, no important electronic devices can be developed using these semiconductors. …”