JAMB - Physics (2000 - No. 25)
In a pure semiconductor, the number of electrons in the conduction band is
less than the number of holes in the valence band
equal to the number of holes in the valence band
greater than the number of holes in the valence band
twice the number of holes in the valence band
Paliwanag
In a pure (intrinsic) semiconductor, the number of electrons in the conduction band is equal to the number of holes in the valence band. This is because when an electron moves from the valence band to the conduction band, it leaves behind a hole.