Identify the correct statement among the following.

The correct answer is Option (4) → The conduction band and the valence band overlap in the case of metals.

The classification of solids is by the energy band gap \( E_g \) between the valence band and the conduction band.

    \( \text{Metals}: \text{bands overlap (no gap)} \)
    \( \text{Semiconductors}: E_g \lt 3\,\mathrm{eV} \)
    \( \text{Insulators}: E_g \gt 3\,\mathrm{eV} \)

Option (1) There is a large energy band gap between the conduction band and the valence band in metals. — Incorrect. In metals there is no gap; the conduction band is partly filled or overlaps the valence band.

Option (2) The energy band gap is nearly or more than \(3\) eV in insulators while the whole conduction band is full of charge carriers. — Incorrect. The gap in insulators is large (more than about 3 eV), but the conduction band is empty, which is why they do not conduct.

Option (3) In semiconductors the energy band gap is more than \(3\) eV. — Incorrect. The gap in semiconductors is small, less than 3 eV (about 1.1 eV for Si).

Option (4) The conduction band and the valence band overlap in the case of metals. — Correct. Because the bands overlap, electrons move freely into empty states, which makes metals good conductors.

NCERT (2026-27):
Classification of Metals, Conductors and Semiconductors – “… The energy band which includes the energy levels of the valence electrons is called the valence band. The energy band above the valence band is called the conduction band. … Normally the conduction band is empty. But when it overlaps on the valence band electrons can move freely into it. This is the case with metallic conductors.”