The process of increasing the conductivity of intrinsic semiconductors by addition of appropriate amounts of suitable impurity is calling doping. Dislocation, Schottky, and Frenkel defects are stoichiometric defects, these are vacancy defects and do not affect the electronic conductivity of the solid. Addition of dopant induces an electronic defect in the parent intrinsic solid which can be positive or negative. The correct answer is (iv).