Question

    Which of the following statements is true about energy

    bands in solids?
    A Forbidden energy gap in metals is very large Correct Answer Incorrect Answer
    B Conductors have overlapping valence and conduction bands Correct Answer Incorrect Answer
    C Insulators have zero forbidden energy gap Correct Answer Incorrect Answer
    D Semiconductors have completely filled conduction band at 0 K Correct Answer Incorrect Answer

    Solution

    In solids, the electrical conductivity depends on the arrangement and occupancy of energy bands. In conductors (metals) , the valence band and conduction band overlap , allowing electrons to move freely even without external energy. This overlap explains their high conductivity, as electrons are readily available for conduction. ●      (A) Incorrect : Metals do not have a large forbidden energy gap; in fact, they have no gap or the bands overlap , allowing free electron movement.

    ●      (C) Incorrect : Insulators have a large forbidden energy gap (typically >5 eV), not zero. Zero gap would imply high conductivity.

    ●      (D) Incorrect : At 0 K , semiconductors have a completely filled valence band and an empty conduction band . The conduction band becomes partially filled only at higher temperatures due to thermal excitation.

    Thus, option (B) correctly describes the band structure of conductors.

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