Which of the following material is a semiconductor?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Silicon
Materials are classified by the size of their electrical conductivity. Conductors (metals and their alloys, graphite) have very large conductivity; insulators (glass, ceramics, Teflon) have very low conductivity. Substances whose conductivity lies between conductors and insulators are called semiconductors; silicon, doped silicon and gallium arsenide are examples, and they are important electronic materials.
Silicon has a conductivity of about \( 1.5 \times 10^{-2}\ \mathrm{S\,m^{-1}} \), far below silver and far above glass, so silicon is the semiconductor.
Why the other options are incorrect
Option (1) Silver — Incorrect. Silver is a metal and one of the best conductors (\( 6.2 \times 10^{3}\ \mathrm{S\,m^{-1}} \) in the book table).
Option (3) Teflon — Incorrect. Teflon is an insulator (\( 1.0 \times 10^{-18}\ \mathrm{S\,m^{-1}} \)); it is used to coat wires and cookware.
Option (4) Glass — Incorrect. Glass is an insulator with very low conductivity.
NCERT (2026-27 edition):
Conductance of Electrolytic Solutions
Table 2.2: The values of Conductivity of some Selected Materials at 298.15 K (rows)
| Material | Conductivity/S m–1 |
|---|---|
| Silver (conductor) | 6.2×103 |
| Glass (insulator) | 1.0×10–16 |
| Teflon (insulator) | 1.0×10–18 |
| Si (semiconductor) | 1.5×10–2 |