Read the following passage and answer the questions.
A student studies a slab of pure silicon. It contains about \(5\times10^{28}\) atoms per cubic metre. The atoms are arranged in a diamond-like structure, and each silicon atom has four valence electrons. Germanium has the same kind of structure. First, the slab is kept in a cold chamber at a temperature very close to 0 K. It is then taken out and allowed to warm up to room temperature (300 K). At this temperature, the intrinsic carrier concentration of silicon is about \(1.5\times10^{16}\ \mathrm{m^{-3}}\). Finally, the student connects a battery and an ammeter in series with the slab. The ammeter shows a small but steady current. The slab is kept at room temperature throughout this test.
Match List-I with List-II.
| List-I | List-II |
|---|---|
| (A) Covalent bond | (I) The fourth orbit \((n = 4)\) |
| (B) Diamond-like structure | (II) A pair of electrons shared by two neighbouring atoms |
| (C) Outermost orbit of a silicon atom | (III) The third orbit \((n = 3)\) |
| (D) Outermost orbit of a germanium atom | (IV) Each atom is surrounded by four nearest neighbours |
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)-(III), (D)-(I)
In silicon and germanium, every atom shares its four valence electrons with its neighbours. The two elements differ in the orbit that holds these electrons.
(A) Covalent bond — This matches (II). Each atom shares one of its electrons with a neighbour and takes a share of one electron from it. The shared pair holds the two atoms together.
(B) Diamond-like structure — This matches (IV). In this lattice every atom has four nearest neighbours, one for each valence electron.
(C) Outermost orbit of a silicon atom — This matches (III). The four bonding electrons of silicon are in its third orbit.
(D) Outermost orbit of a germanium atom — This matches (I). Germanium is a heavier atom, and its bonding electrons are in the fourth orbit.
NCERT (2026-27):
Intrinsic Semiconductor – “… These structures are called the diamond-like structures. Each atom is surrounded by four nearest neighbours. …”
Intrinsic Semiconductor – “… These shared electron pairs are referred to as forming a covalent bond or simply a valence bond. …”
Classification of Metals, Conductors and Semiconductors – “… For Si, the outermost orbit is the third orbit (n = 3), while for Ge it is the fourth orbit (n = 4). …”