Pure silicon and germanium are
(A) conductors
(B) insulators
(C) semiconductors
(D) none of the above

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Hint: Pure silicon and germanium conduct electricity to little extent. The level of electrical conductivity of pure silicon and germanium is in between that of conductors and insulators.

Complete answer:
The electrical conductivity of semiconductors is in between that of conductors and insulators. Insulators do not conduct electricity at all as they have a large energy gap (band gap) between valence band and conduction band. On the other hand, conductors conduct electricity as they have little energy gap (band gap) between valence band and conduction band.
We can improve the conductivity of silicon and germanium by doping.
Doping is the process of adding a small impurity to the crystal. The purpose of this is to increase the electrical conductivity. Silicon and germanium are group 14 elements. We can dope silicon and germanium with group 15 elements such as arsenic. Due to this, the crystal will have excess electrons. This doped crystal is called an n-type semiconductor.
We can also dope silicon and germanium with group 13 elements such as indium. Due to this, the crystal will have holes. This is called a p-type semiconductor. Holes are electron deficiency. The symbol ‘p’ represents the flow of positive charge whereas the symbol ‘n’ represents the flow of electrons.
Pure silicon and germanium are semiconductors.

Hence, the correct option is the option (C).

Note: We can classify semiconductors as intrinsic semiconductors and extrinsic semiconductors. You can convert an intrinsic semiconductor and extrinsic semiconductor by doping.