Define Schottky and Frenkel defects in ionic crystals.

• A. Schottky defects are vacancies of cations only; Frenkel defects are interstitials of anions.
• B. Schottky defects are vacancies of both cations and anions; Frenkel defects are a cation displaced to an interstitial site.
• C. Schottky defects are interstitials; Frenkel defects are vacancies.
• D. Schottky and Frenkel defects are the same type.

Answer: (B)

In ionic crystals, defects that keep overall charge balance are key to understanding diffusion and properties. Schottky defects consist of a pair of vacancies: a missing cation site and a missing anion site, so the lattice loses equal numbers of positive and negative ions and stays stoichiometric overall. Frenkel defects involve a cation moving from its regular lattice site to a nearby interstitial site, leaving behind a vacancy and creating an interstitial ion; this keeps the crystal composition the same but introduces a vacancy–interstitial pair.

This makes the described answer the best: both ion types are missing in Schottky defects, while a cation shifts to an interstitial position in Frenkel defects. The other statements don’t capture both aspects, such as claiming only cation vacancies or saying the two defects are the same.