When a small and suitable amount of Arsenic (As) is added to Germanium, it will become
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → n-type semiconductor
Arsenic is pentavalent (five valence electrons), while germanium is tetravalent. Four electrons of each arsenic atom form covalent bonds with neighbouring germanium atoms; the fifth is loosely bound and is easily donated to the conduction band.
So electrons become the majority carriers and the crystal becomes an n-type semiconductor.
Why the other options are incorrect
Option (2) p-type semiconductor — Incorrect. A p-type semiconductor needs a trivalent impurity such as boron, aluminium, gallium or indium.
Option (3) a p-n junction — Incorrect. A p-n junction needs a p-region and an n-region in the same crystal; adding arsenic alone gives only n-type material.
Option (4) a conductor — Incorrect. A small amount of doping raises the conductivity, but the material remains a semiconductor.
NCERT (2026-27):
Summary – “… n-type semiconducting Si or Ge is obtained by doping with pentavalent atoms (donors) like As, Sb, P, etc., while p-type Si or Ge can be obtained by doping with trivalent atom (acceptors) like B, Al, In etc.”
