The correct statement(s) regarding defects in solids is (are)

(a) Wrong Frenkel defect is favoured when the difference in ionic radii is very large. In the given case Schottky defect is favoured. (b) Correct Frenkel defect arises due to dislocation of smaller ion from its normal lattice point to the interstitial space. (c) Correct When alkali metal in the gaseous state is passed over salts like $\mathrm{NaCl}$, electrons from metal are trapped in the interstitial space giving rise to F-centre defect which is a type of Frenkel defect. (d) Wrong Schottky defect affects physical properties of solids.