The forbidden energy band gap in conductors, semiconductors and insulators are \( E_{G1}, E_{G2} \) and \( E_{G3} \) respectively. The relation among them is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( E_{G1}\lt E_{G2}\lt E_{G3} \)
The energy band gap is the gap between the top of the valence band and the bottom of the conduction band; electrons must cross it to conduct.
\( \text{Conductors (metals): bands overlap, } E_{G1} \approx 0 \)
\( \text{Semiconductors: } E_{G2} \lt 3\,\mathrm{eV} \text{ (Si about 1.1 eV)} \)
\( \text{Insulators: } E_{G3} \gt 3\,\mathrm{eV} \text{ (diamond about 5.4 eV)} \)
So the gap is smallest for conductors and largest for insulators: \( E_{G1} \lt E_{G2} \lt E_{G3} \). This is why a metal conducts easily, a semiconductor conducts when some electrons gain enough energy to cross a small gap, and an insulator hardly conducts at all.
Note: A similar question was also asked in CUET (UG) 2023 on 15-06-2023 (Slot 2).
NCERT (2026-27):
Summary – “… 11. For insulators Eg > 3 eV, for semiconductors Eg is 0.2 eV to 3 eV, while for metals Eg ≈ 0.”