JEE Main 2007 Physics question

Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?

(1)The number of free conduction electrons is significant in C but small in Si and Ge.
(2)The number of free conduction electrons is negligible small in all the three.
(3)The number of free electrons for conduction is significant in all the three.
(4)The number of free electrons for conduction is significant only in Si and Ge but small in C.Correct

Answer: (4)

Solution

Carbon (diamond) has a large band gap (~5.5 eV) and is an insulator, while Si (1.1 eV) and Ge (0.7 eV) are

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Question ID VK-038927