Arrange the following materials in the ascending order of their energ…

The correct answer is Option (4) → A, D, B, C

The energy band gap is the gap between the top of the valence band and the bottom of the conduction band. In a metal the bands overlap (or the conduction band is partly filled), so there is no gap; semiconductors have a small gap and insulators a large one.

    \( \text{(A) Metal: } E_g = 0 \)
    \( \text{(D) Germanium: } E_g \approx 0.7\,\mathrm{eV} \)
    \( \text{(B) Silicon: } E_g \approx 1.1\,\mathrm{eV} \)
    \( \text{(C) Insulator: } E_g \gt 3\,\mathrm{eV} \)

So the ascending order is (A), (D), (B), (C).

NCERT (2026-27):
Classification of Metals, Conductors and Semiconductors – “… One can have a metal either when the conduction band is partially filled and the balanced band is partially empty or when the conduction and valance bands overlap.”

Classification of Metals, Conductors and Semiconductors – “… Case II: In this case, as shown in Fig. 14.2(b), a large band gap E_g exists (E_g > 3 eV). There are no electrons in the conduction band, and therefore no electrical conduction is possible.”

Classification of Metals, Conductors and Semiconductors – “… This is the case of insulators.”

Extrinsic Semiconductor – “… For C (diamond), Si and Ge, the energy gaps are 5.4 eV, 1.1 eV and 0.7 eV, respectively.”