Which of the following statements are correct?

1. A fully occupied band separated from the next (empty) band by a large energy separation (the band gap) leads to the material being an insulator.
2. A band gap occurs when there is a no energy difference between two bands.
3. Electrical conductivity is a characteristic property of partially filled bands of MOs.
4. Overlapping of both bands leads to the material being metallic.
5. Large energy gap between bands leads to the material being semiconductor.

Correct option; Except 1, 3, and 4, all are incorrect statements. A fully occupied band separated from the next (empty) band by a large energy separation (the band gap) leads to the material being an insulator. A band gap occurs when there is some energy difference between two bands. Electrical conductivity is a characteristic property of partially filled bands of MOs. Overlapping of both bands leads to the material being metallic. Large energy gap between bands leads to the material being insulator.