When an impurity is doped into an intrinsic semiconductor, the conductivity of the semiconductor.

When impurity (trivalent or pentavalent) is added into an intrinsic semiconductor, extrinsic semiconductor (p-type or n-type respectively) is obtained. This has increased holes or electrons respectively in conduction band (intrinsic carriers plus the carriers due to impurity). Hence the conductivity of the extrinsic semiconductor increases. Therefore, the correct answer is option A

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