Chemistry - Solid State Question with Solution | TestHub

A Schottky defect is a stoichiometric defect in ionic crystals where cation and anion vacancies are created in such a ratio that electrical neutrality is maintained.
In an MX lattice, the vacancy ratio is 1:1.
In an MX₂ lattice, cation : anion vacancies = 1:2.
In an M₂X lattice, cation : anion vacancies = 2:1.
A random vacancy in any lattice does not necessarily preserve charge neutrality or stoichiometry, so it is not a Schottky defect. Hence, (D) is incorrect.