Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?
- (A)The number of free conduction electrons is significant in C but small in Si and Ge
- (B)The number of free conduction electrons is negligibly small in all the three
- (C)The number of free electrons for conduction is significant in all the three
- (D)The number of free electrons for conduction is significant only in Si and Ge but small in C✓ Correct
Answer: (D)
Solution
The width of the forbidden energy gap decreases on going from carbon to silicon to germanium. Diamond's gap is so wide that almost no electrons are lifted into the conduction band at room temperature, so carbon behaves essentially as an insulator. Silicon and germanium, with much narrower gaps, have appreciable numbers of conduction electrons at the same temperature, which is why conduction is significant in those two but negligibly small in carbon.
JEE Main · 2007 · 29 Apr 2007 · Offline · Single correct option