Which defect leads to decrease in the density of crystal?

Step-by-step solution

In a Schottky defect, an equal number of cations and anions are missing from their lattice sites. This creates vacancies in the crystal structure. Since the number of ions decreases while the volume of the crystal remains effectively constant, the total mass of the crystal decreases. Density is defined as = Z M N_A a^3 . As the mass of the unit cell decreases due to the missing ions, the density of the crystal decreases. Frenkel defect involves ions moving to interstitial sites, which does not change the density. I