To form n-type semiconductor from a pure semiconductor, the impurity to be added is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Arsenic
An n-type semiconductor is made by doping a pure group-IV semiconductor (Si or Ge) with a pentavalent impurity (five valence electrons). Four of its electrons form bonds with the neighbouring atoms and the fifth is free to conduct.
Option (4) Arsenic — Correct. Arsenic is pentavalent, so it donates a free electron and gives an n-type semiconductor.
NCERT (2026-27):
Extrinsic Semiconductor – “… (i) Pentavalent (valency 5); like Arsenic (As), Antimony (Sb), Phosphorous (P), etc.”
n-type Semiconductor – “… Hence in an extrinsic semiconductor doped with pentavalent impurity, electrons become the majority carriers and holes the minority carriers. These semiconductors are, therefore, known as n-type semiconductors.”