At absolute zero, Si acts as

The correct answer is Option (3) → an insulator

Pure silicon is an intrinsic semiconductor with a small energy band gap. At \( T=0\,\mathrm{K} \) there is no thermal energy to break any covalent bond. So every electron stays in the valence band, and the conduction band is empty. With no free electrons and no holes, no current can flow, and Si behaves like an insulator. Only at \( T\gt0\,\mathrm{K} \) does thermal energy lift some electrons across the gap into the conduction band.

NCERT (2026-27):
Intrinsic Semiconductor – “An intrinsic semiconductor will behave like an insulator at T = 0 K as shown in Fig. 14.6(a). It is the thermal energy at higher temperatures (T > 0K), which excites some electrons from the valence band to the conduction band.”

Fig. 14.6: (a) An intrinsic semiconductor at T = 0 K behaves like insulator. (b) At T > 0 K, four thermally generated electron-hole pairs. The filled circles represent electrons and empty circles represent holes.