In an insulator, the forbidden energy gap between the valence band and conduction band is of the order of which of the following?
Answer & explanation
Correct answer: option 1
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