Question

Carbon, silicon and germanium have four valence electrons each. At room temperature the appropriate statement is

• A. The number of free electrons for conduction is significant only in Si and Ge but small in C
• B. The number of free conduction electrons is significant in C but small Si and Ge.
• C. The number of free conduction electrons is negligibly small in all the three.
• D. The number of free conduction electrons is significant in all the three.

Answer 1

Answer: (A)

The number of free electrons for conduction is significant only in Si and Ge but small in C
Option is correct.

In Si and Ge at room temperature($300K$) ; the energy band gap is low as the result of which electrons in the covalent bonds gain kinetic energy, they break the bond and move to conduction band. A hole is also created in the valence band. So the number of free electrons for conduction is significant in Si and Ge. The energy band gap in case of carbon is high as the result of which there are not significant number of electrons in the conduction band even at room temperature.