Read the following passage and answer the questions.
A student measures the resistivity of three unlabelled solids, X, Y and Z, at room temperature. Her readings are about \(1.7\times10^{-8}\ \Omega\,\mathrm{m}\) for X, \(2\times10^{3}\ \Omega\,\mathrm{m}\) for Y and \(10^{14}\ \Omega\,\mathrm{m}\) for Z. She plans to warm each sample a little and take the readings again. To explain her results, she will compare the samples with the energy-band pictures of solids. Such a picture shows a valence band and a conduction band. In some solids the two bands are separated by an energy gap, and the size of this gap differs from one solid to another. She also notes four elements of group IV of the periodic table: carbon (as diamond), silicon, germanium and tin. Each of them has four valence electrons, yet they behave very differently in electric circuits.
Match the group IV elements in List-I with their energy gaps in List-II.
| List-I | List-II |
|---|---|
| (A) Carbon (diamond) | (I) 0.7 eV |
| (B) Silicon | (II) 5.4 eV |
| (C) Germanium | (III) 0 eV |
| (D) Tin | (IV) 1.1 eV |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A)-(II), (B)-(IV), (C)-(I), (D)-(III)
All four elements have the same number of valence electrons. Their electrical behaviour differs because their energy gaps differ. The gap grows in the order tin, germanium, silicon, diamond.
(A) Carbon (diamond) — This matches (II) 5.4 eV. The gap is more than 3 eV, so diamond is an insulator.
(B) Silicon — This matches (IV) 1.1 eV. It is a small gap, as expected for a semiconductor.
(C) Germanium — This matches (I) 0.7 eV. Its bonding electrons are in the fourth orbit and are held less tightly than in silicon, so the gap is smaller.
(D) Tin — This matches (III) 0 eV. With no gap at all, tin behaves as a metal although it is in group IV.
NCERT (2026-27):
Extrinsic Semiconductor – “… For C (diamond), Si and Ge, the energy gaps are 5.4 eV, 1.1 eV and 0.7 eV, respectively. Sn also is a group IV element but it is a metal because the energy gap in its case is 0 eV.”