Concept:In metals, the valence and conduction bands overlap (\( E_g = 0\text{ eV} \)), creating a continuous sea of delocalized conduction electrons without an isolated valence band structure to sustain hole transport.
Formula:$$E_{g,\text{metal}} = 0\text{ eV} \implies \text{Conduction is exclusively electronic } (\sigma = n q \mu_n)$$
Solution:- Hole conduction requires an almost-full valence band separated from the conduction band by a forbidden energy gap \( E_g \).
- Because bands overlap in metals, valence electrons move freely into unoccupied states without leaving behind localized, positively charged covalent bond vacancies.
- Thus, current in metals is carried entirely by free electrons.
Why other options are incorrect:- Option B: All metals contain orbital electrons.
- Option C: Metals have an energy gap of \( E_g = 0\text{ eV} \), not a large forbidden gap.
- Option D: Metals are pure elements or alloys, not doped semiconductors.
Quality & Fidelity Assurance:
Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.