Schottky defect in a crystal arises due to

Metal deficiency defect is shown by $Fe_{0.93}O$. In the crystal,some $Fe^{2+}$ cations are missing and loss of positive charge is compensated by the presence of $Fe^{3+}$ ions. The percentage of $Fe^{2+}$ ions in the $Fe_{0.93}O$ crystals is $....$ (Nearest integer)

Due to vacancy defects,the density of a solid substance .............

Which of the following is $NOT$ true for Schottky defect?

Frenkel defect is generally observed in which of the following?

In spite of long-range order in the arrangement of particles,why are the crystals usually not perfect?