Question

Conductivity of silicon increases by doping it with group-15 elements. Doping means introduction of small amount of impurities like $P, As$ or $Bi$ into the pure crystal.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (B)

If both assertion and reason are true but reason is not the correct explanation of assertion

Answer 2

When a silicon crystal is doped with a group-15 elements, such as $P, A s, S b$ or $B i$ the structure of the crystal lattice is left unchanged but an occasional atom with five valence electrons occupies a site that would normally be occupied by a silicon atom. The foreign atom uses four of its electrons in covalent bonding but the remaining fifth electron becomes delocalised and is thus free to contribute to electrical conduction.