Which of the following statements regarding defects in crystalline solids is correct?

Options

A. Schottky defects exist in non-ionic substances and does not affect density of substance.
B. Frenkel defects increases the dielectric constant.
C. Introduction of impuriy defect in Si by insertion of Al will create n-type semiconductors.
D. The formationi of wustite is an example of metal excess defect.