In an insulator, the forbidden energy gap between the valence band and conduction band is of the order of which of the following?

5 eV

Memory Point !! 

Metals: They possess very low resistivity (or high conductivity).

ρ ~ 10^–2 – 10^–8 Ω m

σ ~ 10² – 10⁸ S m–1

Semiconductors: They have resistivity or conductivity intermediate to metals and insulators.

ρ ~ 10^–5 – 10⁶ Ω m

σ ~ 10⁵ – 10^–6 S m–1

Insulators : They have high resistivity (or low conductivity).

ρ ~ 10¹¹ – 10¹⁹ Ω m

σ ~ 10^–11 – 10^–19 S m–1