Which of the following statement is correct?
A. In conductors, the valence and conduction bands overlap
B. Substances with energy gap of the order of 2 eV are insulators
C. The resistivity of a semiconductor increases with increase in temperature
D. The depletion layer in the pn-junction region is caused by drift of electrons
Choose the correct answer from the options below
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A only
Solids are classified by their energy bands: in metals the bands overlap, in insulators the energy gap is large (more than about 3 eV) and in semiconductors it is small (less than about 3 eV).
(A) In conductors, the valence and conduction bands overlap — Correct. Because the bands overlap, electrons move freely into empty levels, which is why metals conduct.
(B) Substances with energy gap of the order of 2 eV are insulators — Incorrect. A gap below about 3 eV is typical of a semiconductor; insulators have gaps larger than 3 eV.
(C) The resistivity of a semiconductor increases with increase in temperature — Incorrect. Heating breaks more covalent bonds and raises the number of charge carriers, so the resistivity of a semiconductor decreases with temperature.
(D) The depletion layer in the pn-junction region is caused by drift of electrons — Incorrect. The depletion layer forms by the diffusion of electrons and holes across the junction; drift is the motion caused by the field that builds up afterwards.
NCERT (2026-27):
Classification of Metals, Conductors and Semiconductors – “… But when it overlaps on the valence band electrons can move freely into it. This is the case with metallic conductors.”
Summary – “… 11. For insulators Eg > 3 eV, for semiconductors Eg is 0.2 eV to 3 eV, while for metals Eg ≈ 0.”
Resistivity of Various Materials – “… In between the two are the semiconductors. These, however, have resistivities characteristically decreasing with a rise in temperature.”
p-n Junction Formation – “… During the formation of p-n junction, and due to the concentration gradient across p-, and n- sides, holes diffuse from p-side to n-side (p → n) and electrons diffuse from n-side to p-side (n → p). … This space-charge region on either side of the junction together is known as depletion region as the electrons and holes taking part in the initial movement across the junction depleted the region of its free charges (Fig. 14.10).”