AIIMS 2015
- Exam
- AIIMS
- Year
- 2015
- Subject
- Chemistry
- Chapter
- Solid State
AIIMS 2015 · Chemistry · Solid State
Assertion : Conductivity of silicon increases by doping it with...
Assertion : Conductivity of silicon increases by doping it with group-15 elements.
Reason : Doping means introduction of small amount of impurities like , As or Bi into the pure crystal.
Options
- AIf both assertion and reason are true and reason is the correct explanation of assertion.
- BIfboth assertion and reason are true but reason is not the correct explanation of assertion.
- CIf assertion is true but reason is false.
- DIf both assertion and reason are false.
Correct answer
B. Ifboth assertion and reason are true but reason is not the correct explanation of assertion.
Step-by-step solution
When a silicon crystal is doped with a group-15 element like P, As, Sb or Bi, the silicon atoms at some lattice sites are substituted by atoms of group-15 element. Asthese atoms have 5 electrons in the valence shell, after forming normal four covalent bonds with silicon atoms, the extra fifth electron is free and gets delocalized and hence, increases the conductivity of silicon.