Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): In an intrinsic semiconductor, the number of free electrons is equal to the number of holes.
Reason (R): The holes in an intrinsic semiconductor are produced by impurity atoms added to the crystal.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) is correct but (R) is not correct.
Assertion (A) In an intrinsic semiconductor, the number of free electrons is equal to the number of holes. — True. In a pure semiconductor, each covalent bond broken by thermal energy frees one electron and leaves one hole. So \(n_e\) is equal to \(n_h\). This common value is the intrinsic carrier concentration \(n_i\).
Reason (R) The holes in an intrinsic semiconductor are produced by impurity atoms added to the crystal. — False. An intrinsic semiconductor is pure and has no impurity atoms. Its holes are the vacancies left in bonds broken by thermal energy. Trivalent impurities add holes only in a p-type (extrinsic) semiconductor.
NCERT (2026-27):
Intrinsic Semiconductor – “In intrinsic semiconductors, the number of free electrons, ne is equal to the number of holes, nh. …”
Summary – “5. Pure semiconductors are called ‘intrinsic semiconductors’. The presence of charge carriers (electrons and holes) is an ‘intrinsic’ property of the material and these are obtained as a result of thermal excitation. …”